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Thread: Evohome and OpenTherm boiler recommendations?

  1. #1
    Automated Home Legend
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    Default Evohome and OpenTherm boiler recommendations?

    Hi All,

    I know the information on which boilers do and don't play well with Evohome OpenTherm is buried in this forum somewhere, and I've read quite a bit of it in the past (and forgotten more than I read) but a search is failing to turn up what I'm looking for as I suspect it's spread across many threads buried in the middle of threads with seemingly different topics...

    So can those of you actually using Evohome with OpenTherm let me know what boiler brand/series you're using, whether it works 100% or whether there are any caveats or workarounds required?

    My reason for asking is an interesting one - we've found out that we are eligible for a grant to cover (most of) the cost of a new boiler and system due to our circumstances, including the fact the existing system is not far off 30 years old now...

    While it has been fairly reliable, many of the radiators need replacing anyway, it's an open vented system with most radiators on 8mm microbore, a somewhat limescaled heat exchanger and the 74% (when new, probably not now!) efficiency of the boiler is really costing us a fortune in the winter...

    I have no idea how these kind of grants work - we're due for an onsite inspection on Friday to look at the old system and discuss the options, and I have no idea whether we would just be offered a certain model of boiler take it or leave it or whether there is some flexibility there or whether we could contribute a certain amount to for example upgrade to a model that supports OpenTherm, as I'd quite like my next boiler to at least be OpenTherm capable even if I don't use that right away.

    Hence the query about good OpenTherm compatible choices especially in the more budget ranges that they'd be likely to be offering on these kind of grants. I'm not completely wed to the idea of OpenTherm if its going to be too expensive or just not an option - I've never had it before after all... but if I can for minimal extra cost, why not.

    The current boiler is 23kW and is also running a 100 litre hot water cylinder however at 74% efficient that's only about 17kW out at best, and that seems to be enough to heat the house and hot water at the same time. (Just) The current cylinder is too small for the bath in the house now (just barely runs an adequate bath before running cold) and there is no more room for a larger cylinder in the boiler closet and to be honest I'd rather not have Evohome controlling hot water anymore after all the problems the CS92A has given me over the years!!

    So a replacement is almost certainly likely to be a combi-boiler which will simplify the system dramatically. No more cylinder, two open cisterns removed from the loft, two zone valves no longer needed, two BDR91's no longer needed and best of all, CS92A no longer needed. The shower is electric so the boiler is only used for bath and kitchen/bathroom hot taps.

    The boiler lives at floor level in a moderately large closet inside the back porch backing against one of the kitchen walls - a large enough closet that a 100 litre cylinder sits above it anyway. So the new boiler doesn't have to be super compact like one you might fit between kitchen cabinets, and it is out of sight and earshot so noise/looks aren't really an issue either.
    Last edited by DBMandrake; 2nd March 2021 at 01:35 PM.

  2. #2
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    Intergas Xtreme 30. Works 100%

  3. #3
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    Likewise with an Intergas Eco RF 36

  4. #4
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    I am only 3 weeks in with my new boiler - an Intergas Xclusive 36 combi - so still getting used to it. I have connected the OT Bridge with no external temperature sensor. So far all seems to be fine. The Xclusive comes with an OT connection. Bridge used is Honeywell’s paired to my Evohome Control Panel. I suspect the system, i.e. OT and Evohome is still on a learning curve with respect to my house (4 bed detached in the NE) but the first thing I noticed was that it gets rooms up to temperature in similar times across the house and keeps them there. With my old boiler some rooms noticeably heated up quicker than others. I have not adjusted the radiators at all, i.e. done any balancing.

    Oddities with the boiler are the pump starts up on it’s own when there is nowhere calling for heat. Noticeable at night when the heating is off. I don’t know why this should happen and am enquiring. It is not the fail safe function as that switches the pump on only if it has not been on once in the previous 24 hours. Also I noted that if you turn the power off to the boiler it loses its time setting. Surprising that in the 21st century there is no backup battery or facility for it to retain its memory. Not a problem for me as I don’t use it relying on Evohome to control things but I imagine it is a problem for those who use the internal programming function. I am sure something could be wired in to provided backup power. So long as it is better than the backup battery system in the Evohome Control Panel!

    My installer set the flow temperature at 80c believing that is the right setting, or rather he probably left it, it being the default. Research will advise that the boiler is not going to run at full efficiency with that temperature as the return temperature will be too high. I dropped it to 70C to give a return of about 50c and did not notice any difference in the house. Latterly I have dropped it to 65c and it all works fine except that now it does take a little longer for a room to get to temperature. Perhaps about 15 minutes longer. I don’t find that a problem. This morning my living room was at 16.5C when I went in. I set the temperature to 18c and within 10 minutes it was noticeable the chill had gone. Perfectly acceptable for my morning exercising routine. Our helpful man from the Intergas shop has suggested I try dropping the temperature to 55C and see what happens. I will in due course.

    Why Intergas? Some 15 years or so ago, long before I installed Evohome, my service engineer servicing my then Baxi recommended Intergas. He advised they get very few problems with them. Some installers he knew were not installing them because they were not getting maintenance call outs. He retired and recommended another to do the servicing. He also recommended Intergas and told the story of a local club installing an Intergas boiler some years ago which lead to British Gas calling to check believing some fiddling was going on because their gas consumption had plummeted. Probably more to do with how bad their previous boiler was! As time rolled by Intergas, although not widely known about, kept appearing as one of the best, particularly in this forum. As the time came to replace my boiler I did more research and Intergas were/are still coming up high on the list. One independent site, https://www.theheatinghub.co.uk , at the time recommended three makes – Ravenheat, Viessmann and Intergas. I spoke to them about it and they also talked highly of the make. Then I started getting quotes, either installers had not heard of Intergas, or tried to knock them but could not justify their “knocking”. They wanted to install Worcester Bosch. May be because that is all they were familiar with or perhaps got more commission.

    I found a recommended installer in my area on the Intergas site. As to be expected he waxed lyrical about Intergas, said he gets lots of call outs to Worcester Bosch, that the latter are somewhat over engineered and some parts are not so easy to access to replace. The Intergas boiler he assured me is easy to deal with if a part ever needed replacing. Indeed we are told there are only 4 working parts in the boiler. I reached an agreement with him for he to install and I would buy the boiler and bits needed – bought from the IntergasShop (a plug!).

    I have posted elsewhere in the forum about the need or no need for an external expansion vessel for this particular boiler if the system is a large one. It may be something you need to consider. I am having no issues with it. When fired up the pressure goes up but usually to about 1.6 bar, I have seen it at 1.8 bar which I understand is well within safe parameters. I contacted Intergas themselves on the issue for their manual says you must seek their advice. They have not responded.

    Hope this helps.

  5. #5
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    Thanks for the recommendations for Intergas. Not sure if that will be an option with grant funding or whether it will be a "here's what we're offering" situation. Will find out on Friday!

    We have 9 radiators 3 of them being small so I don't think this would count as a large system?

    Is anyone else using a brand other than Intergas with Opentherm who is happy with both the Opentherm compatibility and the boiler itself?

  6. #6
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    I have an Ideal combi boiler with evohome opentherm setup and don’t seem to have any problems.
    I just connected the opentherm bridge, set up the controller to opentherm and let it do what it wanted, not really bothered to look at it as the heating comes on when wanted and the rooms heat up.
    Only have 7 rads controlled with the rad valves and a towel rail set up as the bypass and all seem happy.

  7. #7
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    Quote Originally Posted by G4RHL View Post
    Oddities with the boiler are the pump starts up on it’s own when there is nowhere calling for heat. Noticeable at night when the heating is off. I don’t know why this should happen and am enquiring. It is not the fail safe function as that switches the pump on only if it has not been on once in the previous 24 hours.
    Sounds like this is DHW preheat, have you tried setting it to Eco?

    ► P-on (Program on):
    The appliance's DHW comfort function is switched on continuously within the chosen time slots. In this mode the
    heat exchanger will be kept up to temperature to assure rapid delivery of DHW. If the clock program does not contain any valid switching points, the heat exchanger will continuously be kept up to temperature.

    ► On (Continuous on):
    The appliance's DHW comfort function is switched on continuously. The heat exchanger will be kept up to temperature.

    ► Eco:
    The appliance's DHW comfort function is self learning within the chosen time slots. The appliance will adapt to the pattern of DHW usage. As a result, the temperature of the heat exchanger will
    not be maintained during the night or during long absence. If the clock program does not contain any valid switching points, the self learning feature is maintained.

  8. #8
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    It’s on Eco. Always.

    Talking of DHW my supply leaves a lot to be desired. We are told that a combi gives hot water at mains pressure. It might but I have had to back off showers and taps considerably to get hot water otherwise it comes through warm, luke warm. If not careful the water comes out with force splashing everywhere. We have to remember all the time not to turn the tap much beyond just on. Backing off the flow helps but I cannot do that with the showers other than not turn them other than just on. With that I have had to turn the thermostat up on the shower above its preset temperature in order to get a decent shower. I don't think its the boiler its more balancing the flow. I also don't think there is anything abnormal with my pressure. It will be the same as others on the estate and they so far as aware don't have issues. I will do a pressure check tomorrow. Also may try a flow reducer in the shower feeds. Sadly I don't have an on/off valve in the shower feeds where I can adjust flow. We don't have a bath which is fortunate as it would take an age to fill with hot water. The boiler functions well in all other respects and I have not seen anything in the manual about adjusting flow to the boiler. My stop tap needs to be replaced and I intend to put a flow adjuster in the domestic feed after it feeds the outside tap. If the pressure comes up too high it will be a pressure reducer!

    it may of course be us. We have never ever had a combi boiler and it may be we have to get used to this. In the past we would turn the tap in the shower full on and the pump would start to feed water from the tank. Do that now and one has a cold shower! The showers were fed cold water to mix with the hot from a tank in the loft. Not now though. Methinks I need to back everything off as much as possible but I have two sinks where at present there is no isolation tap I can adjust for that and of course the showers. Isolation controls/pipes are to be installed to those that don't have them but I need to work out how to do that with the showers. In our downstairs WC the filling of the cistern takes precedence over hot water being delivered at the sink. Hence my thinking that it is the house supply to outlets needs adjusting.

    Addendum - 04/03/21
    I checked my water pressure this morning. I took two separate readings. One gave me 92 psi or 6.15 bar, the other 94 psi or 6.2 bar. I guess I need a pressure reducing valve!
    Last edited by G4RHL; 4th March 2021 at 08:02 AM. Reason: Addendum

  9. #9
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    Iíd vote for Intergas too, I fitted one in my last house. Or an Atag.

    Iíve inherited a Vokera in my new house. Out of the box it would default to 80C max flow temperature, so Iíve used an OTGW to optimise. Their newer boilers are more configurable it seems.

  10. #10
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    Not Evohome, but Tado on opentherm with an Ideal Logic combi. Works flawlessly.

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