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Thread: Evohome S Plan BDR91 Boiler Control

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    Default Evohome S Plan BDR91 Boiler Control

    Hi everyone.

    I am a new member, I have been reading some posts, and there is a lot of very useful information here.

    I have just installed an Evohome System with a hot water controller and HR92 radiator controllers into an existing S plan system. I have done it all myself and it is working great despite the installation instructions being a bit vague!

    I am experimenting with the hot water temperature to make sure it gets to between 55-60 degrees, I was a bit worried as the position on my cylinder for the water temp sensor is quite low down so I thought the top of the tank would get much hotter but it seems to be spot on. Incidentally, my old system did not have any kind of water over temperature sensor, should I fit one in case the Evohome system loses comms and carries on trying to heat the water?

    So I have the HR92's set to control the heating zone valve as the old controller did, the valve opens and turns on the pump and the boiler, and when it closes, it switches off the pump and boiler all as it should.

    However, is there any advantage in fitting a third BDR91 relay to control the boiler separately? I worry (probably unnecessarily) that the boiler can be running flat out and when demand stops the valve closes and it shuts the boiler and the pump off when there is a lot of heat left in the boiler. Can or is the Evohome capable of switching the boiler on/off and leaving the zone valve and pump to run on as and when necessary? I do not have any type of pump overrun system and there is a bypass to 2 radiators with no valves fitted.

    I have read some posts about the Evohome modulating the boiler which makes sense rather than it having to run flat out when heat is called for and then suddenly switched off, but this will only work if the Evohome will/can control the zone valve separately and therefore turn the pump on too.

    Also, I need to add some more HR92 radiator valves to existing rooms where I have added 1 but need to add 2 to one room and 1 to 2 other rooms, how do you do add one to a zone after the initial setup? Or do i have to delete my existing zones before adding a new zone to see the option to add more radiator valves at the initial setup?

    The boiler is an oil fired Trianco Eurostar, there are a total of 24 radiators split into 12 zones and some radiators will not have controls but will be set on a low setting for background heat whenever another zone is calling for heat.

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    I am surprised there has been no helpful reply, it seems such a helpful place when reading the forum.

    I have started to get comms faults reported from all my HR92 valves. I have bound all 16 HR92's to a single BDR91 relay box that is controlling the zone valve for the heating. Nowhere have I been able to find out if this is correct, is it OK to bind all my rads to the BDR91 or is that likely to be causing the comms fault?

    I presume the HR92's communicate via the Evohome controller, they all have good RF signal strength of 4's and 5's so I dont think from this it is a comms fault from the HR92's to the controller.

    Any help or advice would be appreciated.

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    Quote Originally Posted by Discojim View Post
    I am experimenting with the hot water temperature to make sure it gets to between 55-60 degrees, I was a bit worried as the position on my cylinder for the water temp sensor is quite low down so I thought the top of the tank would get much hotter but it seems to be spot on. Incidentally, my old system did not have any kind of water over temperature sensor, should I fit one in case the Evohome system loses comms and carries on trying to heat the water?
    About 1/3rd of the way up the cylinder is the recommended location for a temperature sensor. This is so it can sense the cold water coming in the bottom when you run a hot tap and start warming that cold water before all the hot water is used up. If the sensor was at the top then it wouldn't reheat until there was almost no hot water left. Having it lower down ensures continuity of hot water.

    Think about it this way - once about 1/3rd of the hot water is used up it will start to reheat the new cold water in the bottom. The temperature at the top should in theory never get higher than your set point even though you're measuring down low due to convection while the heating coils are hot.

    Is the cylinder vented or un-vented ? If it's vented then you don't really need any additional safety over temperature thermostat, at worst the hot water can never get any hotter than the flow temperature your boiler is set to, and will take a very long time to get there. Realistically it would get to about 5C less than the flow temperature after say an hour.

    My boiler flow temperature (same for both heating and hot water reheat) is set to 70C at the moment so if the hot water zone valve stuck open permanently my hot water would eventually get to about 65C or slightly above. Not enough to cause any harm to the system although there is of course a risk of scalds if it went above 65C.

    If it's an un-vented cylinder then technically you should always have an additional safety stat wired in series with the BDR91 that switches the zone valve.

    So I have the HR92's set to control the heating zone valve as the old controller did, the valve opens and turns on the pump and the boiler, and when it closes, it switches off the pump and boiler all as it should.

    However, is there any advantage in fitting a third BDR91 relay to control the boiler separately? I worry (probably unnecessarily) that the boiler can be running flat out and when demand stops the valve closes and it shuts the boiler and the pump off when there is a lot of heat left in the boiler. Can or is the Evohome capable of switching the boiler on/off and leaving the zone valve and pump to run on as and when necessary? I do not have any type of pump overrun system and there is a bypass to 2 radiators with no valves fitted.
    From the description of no pump overrun, it sounds like you have a very old system boiler, like me. Is your pump externally or internally mounted in the boiler ?

    My system is an old non-condensing system boiler with an external pump which was originally a gravity fed hot water system, and as such had no pump overrun. I converted it to S-Plan and in the process added an external pump overrun timer. Without pump overrun I had problems with kettling - it's just not good for the pump to stop immediately in a TPI controlled system.

    I used an MRT16-REM timer which is readily available:

    https://www.cpelectronics.co.uk/ener...mers/mrt16-rem

    This can do time delays of anywhere from seconds to about 30 minutes depending on how you adjust the controls inside and it is within a tamper-proof face-plate and back box that I mounted right beside my wiring centre box. About 3 minutes would be typical pump overrun time however I ended up using 12 minutes specifically because the TPI cycle time is 10 minutes - this ensures that so long as there is some heat demand the pump does not stop, however after 12 minutes of no demand at all it will stop. I found this worked better than 3 minutes for avoiding kettling, and as I use a modern low energy pump on the lowest speed setting the power penalty for the extra runtime isn't that bad.

    If you're worried about the latent heat in the heat exchanger every time the pump stops during each TPI cycle I'd definitely recommend wiring up an after market pump overrun timer like this, provided there is a bypass in the system.

    Also, I need to add some more HR92 radiator valves to existing rooms where I have added 1 but need to add 2 to one room and 1 to 2 other rooms, how do you do add one to a zone after the initial setup? Or do i have to delete my existing zones before adding a new zone to see the option to add more radiator valves at the initial setup?
    You can just go into the zone config of the existing zone and do the binding process again, for all HR92's that will be in the zone including those that already were. The first one you bind will become the temperature sensor for the zone.
    The boiler is an oil fired Trianco Eurostar, there are a total of 24 radiators split into 12 zones and some radiators will not have controls but will be set on a low setting for background heat whenever another zone is calling for heat.
    I've read that oil fired boilers should be configured to use only 3 TPI cycles per hour instead of the default 6. However you are unable to configure this unless you have a boiler control relay. So even though you don't need a boiler control relay for other reasons, if you want to set the TPI cycles to 3 per hour you may need to get one and configure it.

    In that scenario the orange wires from the zone valves would no longer be used to fire the boiler, instead the third BDR91 would be wired directly to fire the boiler - this is the configuration I have in my system. Having this configuration also allows for the hot water overrun feature to work.

    Quote Originally Posted by Discojim View Post
    I am surprised there has been no helpful reply, it seems such a helpful place when reading the forum.
    Some of us have day jobs...
    I have started to get comms faults reported from all my HR92 valves. I have bound all 16 HR92's to a single BDR91 relay box that is controlling the zone valve for the heating. Nowhere have I been able to find out if this is correct, is it OK to bind all my rads to the BDR91 or is that likely to be causing the comms fault?
    No this is incorrect. I'm not even sure how you've managed it as a BDR91 can only accept 4 bindings anyway.

    You may need to start over and clear all the bindings on the devices - on BDR91's hold the button for over 15 seconds until there is a quick flash, on HR92's go into the bind menu and do a long press on the BIND screen until it says cleared. Then set stored hot water to none and boiler control to none.

    At the moment you don't have a boiler control relay so you should go to stored hot water then bind the hot water temperature sensor, hot water zone valve BDR91 and heating zone valve BDR91 when prompted. Do not try to bind anything else to these BDR91's.

    Then go into each of your zones in the manual zone configuration and rebind your HR92's as "radiator controllers". Hopefully that gets you out of the mess you're in. (I'm not really sure how you would have bound an HR92 directly to a BDR91 - I'm not sure that's possible)

    I presume the HR92's communicate via the Evohome controller, they all have good RF signal strength of 4's and 5's so I dont think from this it is a comms fault from the HR92's to the controller.
    If you've screwed up all the bindings you will get comms faults reported.

    All comms is via the controller, which acts as a comms hubs. So HR92 and BDR91 both talk only to the controller. HR92's never talk directly to a BDR91 and thus should not be bound to one.
    Last edited by DBMandrake; 5th December 2018 at 11:56 AM.

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    Quote Originally Posted by DBMandrake View Post
    go to stored hot water then bind the hot water temperature sensor, hot water zone valve BDR91 and heating zone valve BDR91 when prompted. Do not try to bind anything else to these BDR91's.
    Thank you very much.

    That has been a great help, I could not for the life of me see that setting when I first set it up!

    Who would have thought the Central Heating Zone control valve setting would be under 'Stored Hot Water' settings?? I thought that was only for the hot water zone valve, it makes no snese to put the central heating zone valve under 'Stored' hot water settings????

    But all set up and working great now, thank you again for your help.

    I do think the installation instructions are rather vague, I appreciate it is a lot easier after you have set one up and had to learn the hard way but Honeywell's documentation could be clearer.

    If you're worried about the latent heat in the heat exchanger every time the pump stops during each TPI cycle I'd definitely recommend wiring up an aftermarket pump overrun timer like this, provided there is a bypass in the system.
    Perhaps worry was a bit strong, it more bothers me than worries me that there is wasted heat in the system that could at least be utilised in a towel rail in the bathroom, The boiler has been running with no overrun pump for 12 or more years and it has never been a problem so far.

    From the description of no pump overrun, it sounds like you have a very old system boiler, like me. Is your pump externally or internally mounted in the boiler ?
    Yes, an external pump that simply switches on by the orange wires on the valves that also turns the boiler on, I will look at fitting a timer like you suggest to keep the valves and pump running after the boiler has stopped.

    About 1/3rd of the way up the cylinder is the recommended location for a temperature sensor. This is so it can sense the cold water coming in the bottom when you run a hot tap and start warming that cold water before all the hot water is used up. If the sensor was at the top then it wouldn't reheat until there was almost no hot water left. Having it lower down ensures continuity of hot water.
    That is exactly where I have the sensor, it is a brand new Gledhill unvented tank and there is a tube 1/3rd of the way up to install 2 sensors, I will add an extra overheat sensor as a failsafe, just in case something should ever go wrong with the Evohome sensor, although like you say the boiler temperature cut out should cut out the boiler before any dangerous temperatures are reached.

    No this is incorrect. I'm not even sure how you've managed it as a BDR91 can only accept 4 bindings anyway.
    I see that now but it did allow me to bind each HR92 to the BDR91 and I tested each one and they did activate the relay and and turn on the CH valve and thus turn on the boiler. it all worked fine.....for a few hours at least.

    But a big thank you to you again, you pointed me towards the correct settings and it is all working fine now.

    I am tempted to do some tinkering with the wiring, perhaps have a third boiler control relay to make use of the hot water overrun and then make my own CH pump overrun but not sure if the TPI is a good thing for oil-fired boilers? The wife tells me to stop messing with and leave it all alone!

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    Quote Originally Posted by Discojim View Post
    I do think the installation instructions are rather vague, I appreciate it is a lot easier after you have set one up and had to learn the hard way but Honeywell's documentation could be clearer.
    Yes the binding process is a bit vague in the instructions and is the major source of confusion and problems with self installs.
    Yes, an external pump that simply switches on by the orange wires on the valves that also turns the boiler on, I will look at fitting a timer like you suggest to keep the valves and pump running after the boiler has stopped.
    If you're not seeing any kettling problems with no pump overrun you won't need a long pump overrun. Just 2 or 3 minutes would be sufficient to move latent heat out of the boiler heat exchanger. The timer I suggested is fully adjustable to pretty much any time delay you wish and is simple and easy to wire up as it is designed exactly for applications like pump overrun. (Watch that you set it in the correct mode though, see the instruction PDF)
    I am tempted to do some tinkering with the wiring, perhaps have a third boiler control relay to make use of the hot water overrun and then make my own CH pump overrun but not sure if the TPI is a good thing for oil-fired boilers? The wife tells me to stop messing with and leave it all alone!
    I don't have an oil fired boiler but I've seen it recommended on here including by some members who actually do this for a day job that an oil fired burner is "happier" with only 3 cycles per hour than the default 6 cycles per hour that the TPI in the Evohome does. Whether this is a wear and tear issue I'm not sure.

    Perhaps someone here with an oil fired burner would care to comment.
    Last edited by DBMandrake; 6th December 2018 at 10:29 AM.

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    Thanks for the advice DBMandrake, my Evohome system is working great now. Had it running for about 10 days in all and I am very pleased. Finally being able to zone each room in a big house and being able to control the temperature and times in each zone is brilliant. I now have a load of the old style Honeywell programmable TRV's to sell on eBay!

    I have ordered the timer that you suggested and I do have a third BDR91 relay. I am thinking how best to wire up the overrun timer. Should I keep my existing 2 relay system, one for the hot water controller and one for the central heating and simply use the timer to keep the CH valve and pump running for 5 minutes or so after or should I try and incorporate the third relay to control the boiler independently, in which case should the third relay just switch the boiler on and off and the overrun timer control the pump and the CH valve or should the boiler and pump always be on together for safety and have the overrun on the pump?

    If I knew exactly how the Evohome switched the zones on and off and the boiler it would make it much simpler, ie will it turn on the CH zone valve and the pump at the same time as the boiler relay or is likely to be switching on the boiler without the CH zone valve turned on? Does anybody know this?

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    Just an update in case it may help somebody else in the future.

    I now have a third BDR91 relay to control the boiler independently from the S-Splan zone valves. I have wired a delay timer to the central heating zone valve so that it remains open for 6-7 minutes after the Evohome has asked it to close. This allows water to keep circulating around the central heating circuit of which there are two bathroom radiators without TRV's to make use of any latent heat in the boiler or the pipework.

    I have gone one step further by replacing the circulating pump, a 25+ year-old Grundfos pump with a modern Grundfos Alpha3 Auto Adapt pump, this new pump is brilliant. The old pump was a little noisy and used 150w, this new pump is practically silent and uses a maximum of 48w when all radiators are open but normally only 18w and shuts down to 3w when no demand and automatically senses when to increase the flow, absolutely brilliant, even the wife agrees with that!

    So because the new pump is intelligent, it is always on and circulating some water, even with both zone valves closed it is pumping, but at only 3w current it is only really in standby mode, as soon as a zone valve opens it detects the drop in pressure and increases the flow, as more radiator valves open, again it increases the flow accordingly.

    At night when the heating and hot water zones are closed the pump drops to around 6w of power, it measures the temperature and flow, and when the temperature keeps dropping, it shuts right down to 3w for the rest of the night until the morning when a zone valve opens and it immediately increases the flow again as required. I also bought the Alpha Reader that connects to a smartphone via an app to easily and accurately balance the whole system.

    I have the boiler set to cycle 6 times an hour and run for a minimum of 4 minutes, with this and my 6 minutes time delay on the zone valve there is always warm/hot water running around the CH system to any radiators that might be partially open. I have optimised start and off enabled, it is working really well, it took a few days for Evohome to learn the heating characteristics of each zone and it takes a few days for the Auto Adapt pump to settle down and figure things out, but so far we are all pleased, we have lived in a cold house for years because it was too expensive to heat the whole house, now we are just heating the rooms we use and when we need them. Time will tell if we are actually saving on oil but the house is more comfortable and the boiler seems to be working less hard.

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    Discojim - good to hear about your positive experience with the Alpha 3. I also have one, but didn't enjoy much success with the Auto Adapt mode: the pump would just spiral down towards ever-lower flow rates independently of how many TRVs were open. I suppose this is because the high pressure loss in the pipework convinced the pump that all the valves were closed. Fortunately its constant-pressure mode seems to work better in my system. As you said, it's a very quiet and energy-efficient pump.

    Did you go through the full balancing process using the reader, and if so how did that work out for you (I don't have the reader so haven't had the chance to try that myself).

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    Quote Originally Posted by Ian_W View Post
    Discojim - good to hear about your positive experience with the Alpha 3. I also have one, but didn't enjoy much success with the Auto Adapt mode: the pump would just spiral down towards ever-lower flow rates independently of how many TRVs were open. I suppose this is because the high pressure loss in the pipework convinced the pump that all the valves were closed. Fortunately its constant-pressure mode seems to work better in my system. As you said, it's a very quiet and energy-efficient pump.

    Did you go through the full balancing process using the reader, and if so how did that work out for you (I don't have the reader so haven't had the chance to try that myself).
    As the weather turned colder I did think the radiators were taking a little longer to heat up so I switched the Alpha pump to the Constant Pressure II setting and that seems to be working much better, still shuts down to standby over night.

    I did also buy the Alpha Reader and do the whole balancing process, it took about 3 hours to go around the whole house and complete but I think it was time well spent, there were just 2 radiators I ahve manually tweaked since dong the balancing.

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    I have a similar setup to your initial setup, but now have a spare bdr91 due to having to replace the main controller due to the cleaner breaking my old one. Please could you give details on how you wired your 3rd unit to control the boiler. I have a worcester bosche, with a vented cylinder. This will be upgraded to a megaflow soon due to an imminent loft extension.


    Quote Originally Posted by Discojim View Post
    Just an update in case it may help somebody else in the future.

    I now have a third BDR91 relay to control the boiler independently from the S-Splan zone valves. I have wired a delay timer to the central heating zone valve so that it remains open for 6-7 minutes after the Evohome has asked it to close. This allows water to keep circulating around the central heating circuit of which there are two bathroom radiators without TRV's to make use of any latent heat in the boiler or the pipework.

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