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Thread: Drayton Wiser Open therm

  1. #11
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    Makes for some very interesting reading,I too have a Vaillant 831 Ecotec plus combi.This was installed nearly ten years ago after the Alpha combi that a friend of mine recommended that I had fitted,some friend.After six years of absolute problems year on year with the Alpha,this was ripped out and replaced with the Vaillant.In nearly ten years of ownership the only two problems have been the diverter valve and pressure vessel.The boilers has been serviced every year without fail and I also have the Ady magnaclean which I think are very good.I have recently gone done the road of fitting the Honeywell evohome with Hr92 valves on all rads bar the bathroom towel rad and also have a smiths ss5 plinth heater in the kitchen.Recently I took the plunge on buying the Vaillant Vr33 to be able to use opentherm,this seems to be working very well.The only thing I will say is that my boiler is oversized for our property,one of the most common problem due to the usual thing of an installer not doing his job properly,lesson learnt and noted for the next time we are due a new boiler.I too am very interested in the Intergas boilers,they look very good and with a ten year warranty and less parts to go wrong.There are quite a few people that install these in my area,so when we are ready this might be my choice.Yes Intergas are quite new to the fore but reviews tend to be good and of course opentherm ready,another bonus.

  2. #12
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    Quote Originally Posted by someuser08 View Post
    First of all, thanks for taking time to write all that - very informative. Vaillant is definitely not the worst boiler out there and you have rightly shown that through the history of your installs when compared with WB/Ideal/'Budget'. And you also right about installation/installer to be more important rater than the boiler itself. But in the end its kind of what I expected - you have not installed (or even serviced) Intergas and Atag in numbers that would allow you to objectively compare them with Vaillant that you know inside out. In fact if you were my installer and I have seen where you are coming from I would have probably let you install Vaillant, but if you take 10 random installers of vaillant and compare system they install with 10 random intergas or atag ones, I'm certain it would not be in favor of the former. It maybe not even that the other two boilers are that much better, but installers who chose them do that for a reason (striving to try new things and more versatile in their approach) and could be just better quality heating engineers.
    The fact is I chose not to install Atag or Intergas because I don't believe as a whole package they're a good option. I've serviced a few and I don't like them. It's not just a matter of trying new things, as you can see we've installed a variety of different manufactures over the years. It's from experience that I chose Vaillant as they're what I believe to be the best on the market at this current time. I can't be recommending products to my own customers that I personally don't believe are a good design, don't have a decent manufactures product service, and possibly might not even be around in 10 years time. Look at Rehmeha. They were a commercial brand that ventured into the domestic market, 10 years later they're gone from the domestic market. No warranty support, nothing.


    Quote Originally Posted by someuser08 View Post
    As for my experience with Vaillant 831: I don't know who installed it and how it was serviced within first 4 years, but since year 5 (until year 9 now) we had to change AAV, pressure sensor, filling isolation valves, diverter (twice). None of this is really major, but the cost of parts and labor to fit them (I wish I was gas registered) is getting closer to the original cost of the boiler I think. Since the first time the diverter leaked (and we had to refill the system) I had dosed the inhibitor myself. I also regularly check TF1 filter and nothing major coming out of it (although system is not perfectly clean, that I admit). Diverter leaking again within 2 years - that is just bad design or poor quality of parts.
    All of them things really suggest system contamination. They're all parts that carry water. Just because there's inhibitor in the system doesn't mean it's good to go. AAV leak because they get dirt in them, Pressure sensors are same (Tiny particles clog up the sensor), Filling isolation valves (Contaminated system won't help, however you find on most boilers if you touch the valves after 5 years they will all start leaking!), Diverter - Again contaminated system won't help, however on the early R1 models I think they had some issues with the diverter. As you've had two in a short period i'd be tempted to look into the system more. By contaminated i'm not just talking about dirt, the original installer could have used cleaner in the system and there is traces still in there. Or theres other particles in the system which are floating about which aren't magnetic. Stick any boiler in on a bad system and you will have problems.

    Quote Originally Posted by someuser08 View Post
    On the other hand in my flat 9 years ago Atag A325ECX was installed (I was really lucky with the installer, back then I knew nothing about boilers) and after first year or two I could not get hold of the guy who installed it, so random engineers were coming for yearly service and did nothing apart form safety checks really (also most of the time they said they have never seen or heard of such a boiler). So after 9 years when we had to troubleshoot CO leak from the flue I came across original installer on linkedin and he came around, opened boiler for the first time since installation and was amazed that it looked like it had been in service for just 3 years. This is to me what quality is! Admittedly after initial lift off about 10 years ago, Atag kind of fell out favor with installers because they split into commercial and domestic operations (my boiler actually now belongs to commercial part and still being sold) and new domestic range can only be bought from them directly and even more expensive that it was previously.
    This again rings alarm bells, 9 years and you've got a leaking CO from a flue? Hope you're going to tell me this had nothing to do with the boiler or their own flue system failing and that it was an error caused by someone.

    Quote Originally Posted by someuser08 View Post
    I do not have hands on experience with Intergas, but due to price, simplicity of the design and better support after installation (more people familiar with it than Atag) that would be my first choice now, however due to some flue installation challenges i might still have to go for Atag next time I change my boiler.
    I agree with you on this point, if I had to pick any out the two it would be the Intergas.

    Quote Originally Posted by garymtitley View Post
    Makes for some very interesting reading,I too have a Vaillant 831 Ecotec plus combi.This was installed nearly ten years ago after the Alpha combi that a friend of mine recommended that I had fitted,some friend.After six years of absolute problems year on year with the Alpha,this was ripped out and replaced with the Vaillant.In nearly ten years of ownership the only two problems have been the diverter valve and pressure vessel.The boilers has been serviced every year without fail and I also have the Ady magnaclean which I think are very good.I have recently gone done the road of fitting the Honeywell evohome with Hr92 valves on all rads bar the bathroom towel rad and also have a smiths ss5 plinth heater in the kitchen.Recently I took the plunge on buying the Vaillant Vr33 to be able to use opentherm,this seems to be working very well.The only thing I will say is that my boiler is oversized for our property,one of the most common problem due to the usual thing of an installer not doing his job properly,lesson learnt and noted for the next time we are due a new boiler.I too am very interested in the Intergas boilers,they look very good and with a ten year warranty and less parts to go wrong.There are quite a few people that install these in my area,so when we are ready this might be my choice.Yes Intergas are quite new to the fore but reviews tend to be good and of course opentherm ready,another bonus.
    Two break downs in 10 years isn't bad. The Pressure vessel you could maybe argue that has it been checked and re-pressurised on every service? Not all servicing engineers check this enough, or it could just be that it has failed. I usually find that if their pressures are maintained then they usually last.

    Diverter valves, as I said above I think they had issues on the R1 generation. Which both of yours boilers will be. I would like to think that they've revised the design, and that it won't happen as much.

    As I have said previously, only time will tell with any of these boilers. I'm just basing my opinion on experience of what I have experienced over the years in the industry. You have to remember too, that many of the reviews on the Atag range (maybe not as much on the Intergas) are based on shorter time periods (The boiler is either new, or only 2-3 years old). I wouldn't expect any issues in the first 5 years at all, even if it hadn't been regularly serviced. The time will tell when these boilers are 8 years+ old, then we'll be able to compare.

  3. #13
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    Two break downs in 10years is exceptional,as in that it's nothing and to be perfectly honest I would have expected more issues than I've had,the Alpha I had before it was an absolute nightmare of a boiler and customer service even worse.The Vaillant has been a fantastic boiler.As you have said,the diverter was a well know problem and the newer diverter valve has I believe been made better to avoid the problem.The pressure vessel on my boiler more than likely had never been checked,so can't really blame it,again neglect by the service engineer the main problem.When I do have to replace the Vaillant,I will look at the Vaillant and Intergas in great detail before I decide.One thing I will make sure of is that the new boiler is correctly sized for our house.
    Last edited by garymtitley; 3rd March 2019 at 10:26 PM.

  4. #14
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    Quote Originally Posted by mtmcgavock View Post
    The fact is I chose not to install Atag or Intergas because I don't believe as a whole package they're a good option. I've serviced a few and I don't like them. It's not just a matter of trying new things, as you can see we've installed a variety of different manufactures over the years. It's from experience that I chose Vaillant as they're what I believe to be the best on the market at this current time. I can't be recommending products to my own customers that I personally don't believe are a good design, don't have a decent manufactures product service, and possibly might not even be around in 10 years time. Look at Rehmeha. They were a commercial brand that ventured into the domestic market, 10 years later they're gone from the domestic market. No warranty support, nothing.
    OK, so two things here. First, the design, which is very subjective. Every time gas engineers discuss about what is best its inevitably ends up being a pissing context, so I take individual preferences with a grain of salt. Second, the service. You had great experience with Vaillant, you installed them well and a business model they work well for you, so i don't really see any need for you to try different boilers for the sake of it indeed. However from this position you can't really make statements about overall market. You can only compare apples with apples - you haven't got any knowledge about service from Atag and Intergas and maybe it is just as good and may be if you installed them you would had even less call out than with Vaillant. Who knows. If we had everyone in the industry like yourself - new brands would have never appeared...

    Quote Originally Posted by mtmcgavock View Post
    All of them things really suggest system contamination. They're all parts that carry water. Just because there's inhibitor in the system doesn't mean it's good to go. AAV leak because they get dirt in them, Pressure sensors are same (Tiny particles clog up the sensor), Filling isolation valves (Contaminated system won't help, however you find on most boilers if you touch the valves after 5 years they will all start leaking!), Diverter - Again contaminated system won't help, however on the early R1 models I think they had some issues with the diverter. As you've had two in a short period i'd be tempted to look into the system more. By contaminated i'm not just talking about dirt, the original installer could have used cleaner in the system and there is traces still in there. Or theres other particles in the system which are floating about which aren't magnetic. Stick any boiler in on a bad system and you will have problems.
    Could be I suppose. The system been leaking and re-pressurized so many times that its unlikely anything chemical would have survived by now, but non-metal particles could be an issue. I'm planning to replace the boiler anyway during non-heating season (and I'm researching boilers well over a year now) and it will be cleaned properly. But the fact remains that Vaillant doesn't handle this situation well (and my issues are not unique, lots of them all over internet) and for some reason not for other brands (and I'm not talking just about atag/intergas). Other makes have different common issues as well, but i haven't seen anything en mass for intergas/atag.

    Quote Originally Posted by mtmcgavock View Post
    This again rings alarm bells, 9 years and you've got a leaking CO from a flue? Hope you're going to tell me this had nothing to do with the boiler or their own flue system failing and that it was an error caused by someone.
    Yeah, some muppet (aka as "heating engineer" with several hundreds of positive reviews on a trade website) displaced a sealing ring somehow during a "service" and because leak was really tiny we haven't noticed it until heating season started (it took 8 hours of continuous heating to trip the alarm). These kind of experiences really dent my trust in tradesmen.

    Quote Originally Posted by mtmcgavock View Post
    As I have said previously, only time will tell with any of these boilers. I'm just basing my opinion on experience of what I have experienced over the years in the industry. You have to remember too, that many of the reviews on the Atag range (maybe not as much on the Intergas) are based on shorter time periods (The boiler is either new, or only 2-3 years old). I wouldn't expect any issues in the first 5 years at all, even if it hadn't been regularly serviced. The time will tell when these boilers are 8 years+ old, then we'll be able to compare.
    Atag is actually not new. As i said i had one from the first generation (A/Q ranges) for over 9 years now and it didn't just come out back then so presumably over 10 years now. They still sell it as a commercial boiler, which proves its worth. It was also the very first boiler with a flue recovery system for DHW (secondary hex) on the UK market and many are only following suit now. The newer IC/IS range is only about 4 years old now, but this is probably a reasonable time to give it to develop. I personally would not have boiler installed that came out over 5 years as by the end of its useful life (10 years) it would be 15 years old technology which in current tech world is ages (they even could ban gas boilers by then, lol).

    Anyway back to OP's post - why would anyone (especially with smart heating system) consider in 2019 a new boiler that doesn't have an opentherm (and really what were Vaillant thinking)?

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    Quote Originally Posted by someuser08 View Post
    If we had everyone in the industry like yourself - new brands would have never appeared...
    I think that's a bit of a harsh comment. We're always open to trying new things, and i've tried different brands over the years in boilers. Most heating engineers wouldn't even know what Evohome is, try getting one to fit the system! So i'd say we're pretty up to date thanks.



    Quote Originally Posted by someuser08 View Post
    Other makes have different common issues as well, but i haven't seen anything en mass for intergas/atag.
    Simple answer, it's because they haven't been installed in the same numbers.



    Quote Originally Posted by someuser08 View Post
    These kind of experiences really dent my trust in tradesmen.
    Just because you've had one bad experience doesn't mean we're all the same!



    Quote Originally Posted by someuser08 View Post
    Atag is actually not new. As i said i had one from the first generation (A/Q ranges) for over 9 years now and it didn't just come out back then so presumably over 10 years now. They still sell it as a commercial boiler, which proves its worth. It was also the very first boiler with a flue recovery system for DHW (secondary hex) on the UK market and many are only following suit now. The newer IC/IS range is only about 4 years old now, but this is probably a reasonable time to give it to develop. I personally would not have boiler installed that came out over 5 years as by the end of its useful life (10 years) it would be 15 years old technology which in current tech world is ages (they even could ban gas boilers by then, lol).
    Actually if you'd read my post properly you'd realise I never said Atag were new. As you've stated the IC/IS range has only been out about 4 years, this is when they really started push the domestic side of the business. With this more people installed them, public became aware of them more. My point was that anyone reviewing the IC/IS range could only have had it fitted 4 years tops. In this time period (We'll take Vaillant as an example seeming you think they're so bad!) I wouldn't expect anyone to have had any issues with their boilers. So you go a write a review of your 10 year old Vaillant (Slating it) then read a review for a 4 year old Atag. You aren't comparing Apples to Apples as you say


    Quote Originally Posted by someuser08 View Post
    Anyway back to OP's post - why would anyone (especially with smart heating system) consider in 2019 a new boiler that doesn't have an opentherm (and really what were Vaillant thinking)?
    Simple, Vaillant wants you to use their own controls that basically do Opentherm using the eBus system. Actually they've been well ahead of the game for a good few years with this, when using the Vaillant Controllers and wiring centres. HW priority, adapting flow temps. They even do their own Radiator controllers, so I suspect that this is why they haven't adopted Opentherm.

    Also referring to other manufactures there's that many issues with Opentherm across the board (Viessmann and Ideal) that I can see why someone wouldn't want the hassle of using it. And really, is it only beneficial in a house that's multi zoned?

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    Having started this thread, I've been impressed with the very detailed responses from mtmcgavock particularly his experience of installing boilers, whilst I appreciate if I choose a Vaillant I won't be able to use Opentherm, I do have an investment in Drayton Wiser and like the App for setting differential room temperatures and being able to set these remotely, am I likely to have an issue interfacing this with a Vaillant boiler controller?

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    Quote Originally Posted by njr001 View Post
    Having started this thread, I've been impressed with the very detailed responses from mtmcgavock particularly his experience of installing boilers, whilst I appreciate if I choose a Vaillant I won't be able to use Opentherm, I do have an investment in Drayton Wiser and like the App for setting differential room temperatures and being able to set these remotely, am I likely to have an issue interfacing this with a Vaillant boiler controller?
    Thanks. No in this case you wouldn't use/require the Vaillant Controller and just use the S/L on the boiler. So it would just be an On/Off and you'd have to set the required flow temperature on the boiler as you saw fit.

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    Quote Originally Posted by mtmcgavock View Post
    Also referring to other manufactures there's that many issues with Opentherm across the board (Viessmann and Ideal) that I can see why someone wouldn't want the hassle of using it. And really, is it only beneficial in a house that's multi zoned?
    Opentherm has nothing to do with single zoned or multi-zoned. It can work with either and doesn't care.

    It's just a better (smoother, more efficient, more precise, quicker) way to control the heat demand sent to the boiler instead of repeatedly switching it on and off, which is kinda.... crude, to say the least, especially in 2019...

    It makes a lot more sense with today's modulating boilers because it allows the boilers own modulating system to achieve the target flow temperature.

    If the boilers maximum flow temperature is set to 70C but the thermostat thinks 50C flow temperature is appropriate at a given moment it asks for that and the boiler modulates its burner to achieve that - full burn if its a long way below it to get there quickly, reduced burn when it gets near 50C, and modulating to try to maintain a nice steady 50C.

    Response time for changes in demand is also fast - if the thermostat now decides that 60C is needed because someone left some doors open or adjusted a set point it sends that new heat demand and the boiler will act on it instantly striving to get to 60C as soon as it can and stay there.

    Swap that out for a relay doing TPI and things get a whole lot worse.

    Firstly you now have the issue that the boiler is unaware of the flow temperature that the thermostat would like. All it knows is that its max flow temperature is set to 70C by the dial on the front, and it is getting turned on and off a lot. When it's commanded on it does its best to get to 70C.

    Lets say that room temperature equilibrium at a set point of 20C demands an average flow temperature of 50C as before. Through negative feedback the thermostat will eventually learn the on/off duty cycle that achieves the steady 20C room temperature, and that will be an average of 50C flow temperature. But the thermostat doesn't know what the flow temperature is... all it knows is the duty cycle. Neither thermostat or boiler know what the average flow temperature should be for the situation.

    To maintain that average 50C it has to keep switching the boiler off before it gets to its 70C set point. So it perhaps oscillates between 40C and 60C in each TPI cycle. During every on cycle the boiler will be going at full burn trying to get to the 70C flow temperature set point that it is never allowed to get to.

    The modulating boiler never gets a chance to modulate when TPI heat demand is low! It also goes through a lot of unnecessary on/off cycles where the striker is having to light the flame. Every time it gets lit it probably generates excess CO and HC for a couple of seconds as well.

    Compare this to Opentherm asking for a constant 50C with the burner running constantly at a low output.

    Secondly, there isn't even a fixed relationship between TPI duty cycle and average flow temperature! It depends on the load on the boiler, eg how many radiators are open and by how much. If you have more radiators open it will take a higher TPI duty cycle to get the same average flow temperature, while only one or two radiators open will need a low duty cycle to achieve a given flow temperature.

    Thus there is a lot of interaction between different zones - more load from additional zones requesting heat will drag the average flow temperature down so the thermostat will have to find a new duty cycle to bring the average flow temperature back up to where it needs to be (which takes time) while with Opentherm the boiler will automatically adjust its heat output to regulate the flow temperature to the requested temperature despite changes in load.

    Thirdly response time is really poor with TPI. Typical TPI cycles are 10 minutes long, that means the heat demand is only an average over a 10 minute period, so it takes at least 10 minutes on average for a change in heat demand sent by the thermostat to actually have any real effect on the heat output of the boiler and radiator panel temperatures. This additional lag makes the system unresponsive to changes like doors being opened and closed, small changes in set point etc.

    For example on my system (TPI) if I increase the set point in a room at equilibrium by half a degree and the current heat demand of the room is quite low it can take over 30 minutes for any appreciable change in room temperature to occur. The first 10 minutes is wasted by the lag of TPI. My biggest issue with TPI is the poor response time.

    Compare that to Opentherm where any change in requested flow temperature no matter how small (say 5C) will be responded to by the boiler immediately and within maybe a couple of minutes the water temperature flowing through the radiators has increased. This faster response time leads to faster overall system response time to changes in set point or room conditions, less overshooting etc...

    I don't doubt that there are significant problems with the implementations of Opentherm in some systems, with compatibility issues etc... but the fundamental premise of a thermostat digitally requesting a specific flow temperature is absolutely sound, absolutely superior than TPI in multiple ways, and is just as applicable for a single zone system as multi-zone.

    I just wish manufacturers would get off their behinds and implement it properly and fix all the silly compatibility issues! It's not rocket science!
    Last edited by DBMandrake; 9th March 2019 at 11:23 AM.

  9. #19
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    Quote Originally Posted by DBMandrake View Post
    Opentherm has nothing to do with single zoned or multi-zoned. It can work with either and doesn't care.

    It's just a better (smoother, more efficient, more precise, quicker) way to control the heat demand sent to the boiler instead of repeatedly switching it on and off, which is kinda.... crude, to say the least, especially in 2019...

    It makes a lot more sense with today's modulating boilers because it allows the boilers own modulating system to achieve the target flow temperature.

    If the boilers maximum flow temperature is set to 70C but the thermostat thinks 50C flow temperature is appropriate at a given moment it asks for that and the boiler modulates its burner to achieve that - full burn if its a long way below it to get there quickly, reduced burn when it gets near 50C, and modulating to try to maintain a nice steady 50C.

    Response time for changes in demand is also fast - if the thermostat now decides that 60C is needed because someone left some doors open or adjusted a set point it sends that new heat demand and the boiler will act on it instantly striving to get to 60C as soon as it can and stay there.

    Swap that out for a relay doing TPI and things get a whole lot worse.

    Firstly you now have the issue that the boiler is unaware of the flow temperature that the thermostat would like. All it knows is that its max flow temperature is set to 70C by the dial on the front, and it is getting turned on and off a lot. When it's commanded on it does its best to get to 70C.

    Lets say that room temperature equilibrium at a set point of 20C demands an average flow temperature of 50C as before. Through negative feedback the thermostat will eventually learn the on/off duty cycle that achieves the steady 20C room temperature, and that will be an average of 50C flow temperature. But the thermostat doesn't know what the flow temperature is... all it knows is the duty cycle. Neither thermostat or boiler know what the average flow temperature should be for the situation.

    To maintain that average 50C it has to keep switching the boiler off before it gets to its 70C set point. So it perhaps oscillates between 40C and 60C in each TPI cycle. During every on cycle the boiler will be going at full burn trying to get to the 70C flow temperature set point that it is never allowed to get to.

    The modulating boiler never gets a chance to modulate when TPI heat demand is low! It also goes through a lot of unnecessary on/off cycles where the striker is having to light the flame. Every time it gets lit it probably generates excess CO and HC for a couple of seconds as well.

    Compare this to Opentherm asking for a constant 50C with the burner running constantly at a low output.

    Secondly, there isn't even a fixed relationship between TPI duty cycle and average flow temperature! It depends on the load on the boiler, eg how many radiators are open and by how much. If you have more radiators open it will take a higher TPI duty cycle to get the same average flow temperature, while only one or two radiators open will need a low duty cycle to achieve a given flow temperature.

    Thus there is a lot of interaction between different zones - more load from additional zones requesting heat will drag the average flow temperature down so the thermostat will have to find a new duty cycle to bring the average flow temperature back up to where it needs to be (which takes time) while with Opentherm the boiler will automatically adjust its heat output to regulate the flow temperature to the requested temperature despite changes in load.

    Thirdly response time is really poor with TPI. Typical TPI cycles are 10 minutes long, that means the heat demand is only an average over a 10 minute period, so it takes at least 10 minutes on average for a change in heat demand sent by the thermostat to actually have any real effect on the heat output of the boiler and radiator panel temperatures. This additional lag makes the system unresponsive to changes like doors being opened and closed, small changes in set point etc.

    For example on my system (TPI) if I increase the set point in a room at equilibrium by half a degree and the current heat demand of the room is quite low it can take over 30 minutes for any appreciable change in room temperature to occur. The first 10 minutes is wasted by the lag of TPI. My biggest issue with TPI is the poor response time.

    Compare that to Opentherm where any change in requested flow temperature no matter how small (say 5C) will be responded to by the boiler immediately and within maybe a couple of minutes the water temperature flowing through the radiators has increased. This faster response time leads to faster overall system response time to changes in set point or room conditions, less overshooting etc...

    I don't doubt that there are significant problems with the implementations of Opentherm in some systems, with compatibility issues etc... but the fundamental premise of a thermostat digitally requesting a specific flow temperature is absolutely sound, absolutely superior than TPI in multiple ways, and is just as applicable for a single zone system as multi-zone.

    I just wish manufacturers would get off their behinds and implement it properly and fix all the silly compatibility issues! It's not rocket science!
    I understand how Opentherm works and i've fitted Evohome systems with it. Yes it is the way forward and I do think it's a great idea. As i've said Vaillant to an extent have been doing this on their own controllers for a while but what I was getting at in my last post regarding the Single/Multi Room zoning was that Opentherm in a Single Zone application really isn't always the best way forward.

    For instance, you have the Single Zone stat located in the Hall. The hall either heats up quicker than other rooms, or slower. Stat then realises this, adjusts flow temperature accordingly, either lowers or increases as it sees fit. So you've got an adapting flow temperature now to maintain the heat in that Single zone where the stat is. The bedroom upstairs which is North Facing (Maybe with an undersized radiator for condensing boiler) is pretty chilly now as it's only getting a low flow temperature to get that room to a decent temperature. Or the other way zones which are heated up, but the stat is requesting a higher flow temperature are now overshooting. Yes you could argue that it's only the same as TPI to a degree, but at least for certain periods it's getting the flow temperature that is set at the boiler. In terms of efficiency it might be great for that single zone, but in terms of comfort for other areas in that property you might be decreasing it.

    That is kind of the point I was trying to make. A Multi Zoned system, yes Opentherm all the way. But personally I don't think that in a Singe zone application it is the best solution. You also have to consider that Evohome even asks for 100% temperature when a zone is 1.5oc out. Many of my own zones come on at different times of the day to various temperatures. I could probably guarantee that a zone is out 1.5oc during heating periods, so it'd be asking for 100% demand anyway. Also add in the fact that most boilers only have a 1:4 to 1:6 modulation range, so if the boiler has been oversized for the property (Which most installers seem to do!) then you are only going to be modulating down to a 3kw output.

    In my own property I actually find TPI works quite well, I have a non modulating boiler which is either On or Off. Now whether this helps as you're only getting a constant heat output out of it, i'm unsure. But I rarely suffer from overshoots or zones taking time to meet set points.

    Opentherm is the way forward no doubt and it's something I would have when I come to replace my boiler, but I think we've got a long way to go before it is a viable option for installers to pick.

  10. #20
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    And back to OP's first post again - I was actually told that Vaillant no longer consider VR33 invalidating warranty as long as it's removed before warranty service guys come to sort out any issues. So if your installer removes it before calling Vaillant then it should be OK...

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