Evohome woes

[graham.gibson]

I recently fitted Evohome to an S plan system – Worcester Bosch 30CDi conventional boiler, Grundfos Alpha2L pump, Honeywell 2 port zone valves and Honeywell ABV – all about 2 years old. HR92s on all rads. BRD91 as heating valve controller and second BDR91 as hot water valve controller. 12 out of 15 rads have Danfoss RA/VL TRVs with the HR92 adapters. Boiler temp is set to 60 degrees.

On the one hand, things are mostly ok – hot water and internet control are perfect and the setpoints are largely maintained in each zone. Sometimes the temp in a zone falls well below setpoint and I have to reset the corresponding HR92 – I suspect this is a symptom of my Danfoss RA/VL valve bodies being old. I have managed to resolve quite a few niggles along the way (and many thanks to Richard from Evohome Shop who has been extremely helpful), but I have a further niggle and I thought I would reach out to the experts on this forum for advice.

If I reduce the temp in all zones, the TRVs turn off, but the heating BDR91 remains on for some time before turning off. The BDR91 then comes on from time to time, presumably to keep the temp ‘topped up’ in the zones (or perhaps for some other reason). However, I've noticed in some cases that my heating return pipe remains cool and instead the hot water just circulates round the bypass loop. I don’t know if this is because the HR92s think that they are opening but the underlying RA/VL(s) are not actually opening, or if the HR92s are opening partially such that the flow in the heating circuit is very low and the bypass kicks in to maintain minimum flow rate, or if the BDR91 is firing incorrectly when there is no demand (or some combination of these). When the system is in this state, the boiler gets into a constant cycle of firing up, heating to 60 degrees, going off, water then rises to around 67 degrees as heat is only being dissipated via the bypass loop, cools down below 60 then the boiler fires up again then repeat.

What’s troubling me is that when the system gets into this state, all that appears to be happening is that the bypass loop is being heated all night, which seems to be a waste of energy to me and also unnecessary repeated firing of the boiler.

I’d welcome any advice on how to definitively troubleshoot this issue. I’m concerned that I’ll have to replace all of my RA/VLs (which is a complete pain as I’ll have to extend the pipework at each rad) or continually waste energy or return to a single zone configuration using a room stat and no TRVs in that room (which would be a waste of Evohome’s capabilities).

Thanks,
Graham

[rotor]

It sounds like something that happened to me early on. One of the HR92 is asking for heat; you need to figure out which one it is, and why. In my case the TRV valve was stuck shut, so the HR92 kept asking for heat because the room was colder than it wanted it to be and it wasn't warming up because hot water wasn't flowing.

Second thing, do you have any radiators without TRV/HR92? If so, then the water should still be able to flow through there, in which case your ABV may be set too "weak" and is triggering too easily, if that makes sense. I just recently tightened my ABV, which fixed a very noisy bathroom rad on the top floor -- I suspect the weight of the water was overcoming the ABV. It's now set to 5.2-ish (meters H2O).

Even if you tighten the ABV, you can still tell it is working when your Heating valve closes down. In my case, the pump on the boiler keeps going for another 15-20 seconds, and you can hear the water flowing through the ABV at that point.

The way I figured out how tight to make the ABV, was late at night (nice quiet house), with my ear right next to it (don't touch it with your ear, it's hot!), with the CH and boiler going, I started closing it until a hissing sound stopped. I then re-opened it a bit, and the hissing started again. So essentially I tightened it so there was no hissing, and hopefully that's job done.

My logical view is that there should be no water flowing through the ABV under normal operation, but rather only when flow is severely restricted (e.g. when all the TRVs are closed, the CH valve is closed).

[theasman]

My system is identical to the OP and shows exactly the same symptoms.

Before doing a final install I had all the HR92s on the bench so could see that they had all closed correctly but the heating BDR91 would still randomly call for heat. After many calls to Honeywell support they concluded that the controller was faulty. This was replaced together with the CH BDR91 but the spurious firing remains. My conclusion was that one of the HR92s may be faulty but whenever a single HR92 is asked to increase temperature and then reduced again the heating BDR91 works as it should.

The system is now fully installed but still shows this random boiler turn-off/firing. I can find no way of being able to trouble shoot what is causing this and can only conclude this is an inherent fault with the Evohome system and finding another user with the same symptoms reinforces this conclusion.

Tony

[MrB]

Just to add a footnote to this:

This is the reason multiple people have requested an indicator, per HR92, to show when it is requesting heat.
Even the software API is broken because it always reports "OFF" for all HR92's - which the whole world would agree is utterly pointless.

If this simple bit of information was visible/available it would make this kind of problem tracking infinitely easier.

[paulockenden]

The API must have it, because I'm sure Mavis said that Smarthings reports what's calling for heat (not sure whether it's at zone or device level). And Smartthings is using the API.

P.

[Mavis]

The API must have it, because I'm sure Mavis said that Smarthings reports what's calling for heat (not sure whether it's at zone or device level). And Smartthings is using the API.

P.

Yes I can confirm that in SmartThings each individual room shows either 'idle' or 'heating to xc.' (Where x is the set point temp.) I only have 1 rad in each room so can't confirm if zones or devices.

[graham.gibson]

Thanks for the reply folks. It's good to know (in a sense) that it's not just me experiencing these types of issues, but I guess it doesn't help us to resolve the problem and feel more confident about the system. Sometimes I think that Evohome is trying to be too clever for its own good, especially given the wide range of TRVs and system configurations that it needs to support. If it did a full open / full close of each TRV and only fired the BDR91 when there was demand from a zone then I think that some of these problems would be avoided. It's the partial opening of the HR92s and the regular firing of the BDR91 even when there is no heat demand from a zone that don't make any sense to me. I'm torn now between reverting to a single heating zone with a room stat and no TRVs or replacing all of my TRV bodies in the hope that this might help, even though it might not. I bought a Honeywell Valencia body to try but I don't think I'll be going for those given the additional complexity of a balancing insert which is yet another thing to play around with (it affects pin travel).

[paulockenden]

How recent is "recently fitted"? It might be that your system is still in learning mode.

I find it's best not to tinker while that is happening.

P.

[graham.gibson]

Fitted about 2 weeks ago.

Regards,
Graham

[paulockenden]

Ah - in that case let it learn for a bit longer.