EvoHome + Opentherm certified boilers

[hy288]

Hi all,

I'm planning to install Honeywell Evohome for zoned heating control and want to pair it with a system boiler that supports OpenTherm effectively. However, it seems that even with OT-certified boilers, the real-world compatibility varies — especially in terms of feature support and control behaviour.
From what I’ve gathered, some boilers offer only basic OpenTherm functionality, while others integrate more fully. Unfortunately, this isn’t well documented and tends to rely on installer experience or community feedback.

Currently I’ve been looking at the following boiler list:

• Ideal Vogue MAX system boiler - Vogue Max System Boiler | 15, 18, 26, 32KW System Boilers (preferred choice?)
• Ideal Logic MAX system boiler - Logic Max System Boiler - 15, 18, 24 & 30kw Model
• Baxi 800 System 2 boiler - Baxi 800 System 2 | Gas System Boilers
• Intergas HRE SB system boiler - HRE SB - Compact Boiler - Heating Only - Intergas Heating
• Intergas Xclusive - Xclusive - Intergas Heating

I'm particularly looking for feedback from anyone using Evohome over OpenTherm with any of these boilers (particularly Ideal Vogue) :

• Does it work reliably for central heating (no odd behaviour)?
• Does modulation behave smoothly (no short-cycling or overshooting)?
• Have you explored OpenTherm feedback data via a gateway (e.g., OTGW)?
• Are any advanced OpenTherm features visible in platforms like Homey or Home Assistant?

OT Features of interest being:

Feature​	Description​
CH Setpoint Control	Evohome dynamically sets flow temp based on zone demand.
CH Flow Temp Reporting	Boiler sends actual flow temp (useful for monitoring).
Modulation Ratio	Boiler’s turn-down ability (impacts efficiency and cycling).
Boiler Status Feedback	Provides burner state, operating mode, etc.
Flame Status Reporting	Indicates if the burner is firing.
System Pressure Reporting	Reports water pressure (if supported by boiler).
Fault Code Reporting	Sends fault/error codes back to the system (for Homey/HA alerts).
Boiler Lockout Reset	Allows remote reset of boiler faults (rare but useful).

If you’ve had experience combining Evohome with any of these boilers over OpenTherm, I’d love to hear your insights — both positive or otherwise. I'm especially curious which boilers offer the richest OT feature support (even if Evohome itself doesn’t expose it — I’m interested in consuming this through automation/monitoring via OTGateway).

Thanks in advance!
Hung

 

[muggles]

Intergas OT integration is excellent. The SB's modulation is poor, but the Xclusive is worth looking at.

 

[vulcancontinental]

I work for a boiler manufacturer that when tested the evohome did not work with smoothly as the boiler requires an instruction from Evo to adjust DHW temp which it couldn't do however I could answer some other of your questions.

Yes, it sends and adjusts flow temp plus also return, DHW , and flue temps.

Modulation is built into the boiler not evohome.

Yes to operating state, firing and pressure.

Yes to alarm reporting.

I'm not aware of any now that permit remote reset of a boiler lockout by app. Our earlier control did but I think any manufacturer is wary or restarting a gas appliance from another country by internet. Reset from the control in the property is still available.

Much of OT capability is underused, e.g. I can repressurise my system from the room control and there are lots of unused instructions.

I did tests on my boiler reading fuel consumption and compensating for external conditions with OT, OT plus boiler WC, OT plus the OT weather comp and WC alone. There was a 1.5% efficiency improvement with OT plus WC but comfort was not as good as two temp WC on its own so I stick with that.

I also ran the OT monitor on my previous aluminium boiler and it was a joy to watch the consistency. Don't discard flow to return temps and room temps but also
look for return to flue temp differences, that tells you how good the heat exchanger is, the closer the better.

 

[hy288]

I work for a boiler manufacturer that when tested the evohome did not work with smoothly as the boiler requires an instruction from Evo to adjust DHW temp which it couldn't do however I could answer some other of your questions.

Yes, it sends and adjusts flow temp plus also return, DHW , and flue temps.

Modulation is built into the boiler not evohome.

Yes to operating state, firing and pressure.

Yes to alarm reporting.

I'm not aware of any now that permit remote reset of a boiler lockout by app. Our earlier control did but I think any manufacturer is wary or restarting a gas appliance from another country by internet. Reset from the control in the property is still available.

Much of OT capability is underused, e.g. I can repressurise my system from the room control and there are lots of unused instructions.

I did tests on my boiler reading fuel consumption and compensating for external conditions with OT, OT plus boiler WC, OT plus the OT weather comp and WC alone. There was a 1.5% efficiency improvement with OT plus WC but comfort was not as good as two temp WC on its own so I stick with that.

I also ran the OT monitor on my previous aluminium boiler and it was a joy to watch the consistency. Don't discard flow to return temps and room temps but also
look for return to flue temp differences, that tells you how good the heat exchanger is, the closer the better.

Thanks again for your detailed response — really appreciated.

Just to share my understanding on the DHW side (with a hot water tank): Evohome manages DHW using the CS92 cylinder sensor and a BDR91 relay to control the zone valve. Evohome doesn’t send a specific DHW temperature setpoint over OpenTherm — I think it just sends an on/off heat request when the CS92 reports the cylinder is below its target temp. The boiler then fires at its default DHW temp (e.g. 60°C). So I wouldn’t expect Evohome to control DHW temp via OpenTherm in this setup — it’s intentionally designed to control DHW externally via relay logic and sensor feedback, rather than passing a temperature setpoint to the boiler.

You mentioned that Evohome didn’t work smoothly with your boiler because it couldn’t send a DHW setpoint — I’m guessing that was with a boiler designed to expect full OpenTherm control of DHW, rather than external control via zone valve and sensor?

Also, if you don’t mind me asking — which boiler model were you testing Evohome with? I’m currently looking at Ideal Vogue Max, Baxi 800 System 2, and Intergas Xclusive, so knowing whether your test boiler was one of those would really help me make sense of the comparison.

I was also really interested in your comment about flow, return, flue temps, modulation, pressure, and fault codes being available. Were you seeing those via an OpenTherm Gateway or Home Assistant/Homey, or were those values exposed directly through the boiler or Evohome? I’m curious how much of that data is actually exposed when Evohome is used vs. what needs a more advanced monitoring setup.

Finally, on your weather compensation test — that was fascinating. Were you using the boiler’s own outdoor sensor, or was it integrated through OpenTherm? I’ve read some boilers prioritise their internal WC logic over OpenTherm setpoints when both are active, so would love to know how yours behaved.

Thanks again — this kind of insight is gold when trying to spec the right boiler/controller combination.

 

[vulcancontinental]

Thanks again for your detailed response — really appreciated.

Just to share my understanding on the DHW side (with a hot water tank): Evohome manages DHW using the CS92 cylinder sensor and a BDR91 relay to control the zone valve. Evohome doesn’t send a specific DHW temperature setpoint over OpenTherm — I think it just sends an on/off heat request when the CS92 reports the cylinder is below its target temp. The boiler then fires at its default DHW temp (e.g. 60°C). So I wouldn’t expect Evohome to control DHW temp via OpenTherm in this setup — it’s intentionally designed to control DHW externally via relay logic and sensor feedback, rather than passing a temperature setpoint to the boiler.

I work for Vokera. I think it's 86% of what we sell are combination boilers so brining in the OT for system boilers wasn't a starter for us although we sell it abroad. DHW on a combi on our boilers has to be from the control, the selector is disabled on our combi boilers, not on all other brands.

It's perfectly possible to control DHW by OpenTherm with a system boiler but I have used EPH controls to do just that. Set the maximum reheat temperature required on the control and that is locked then when space heating is required the flow temperature is modulated. Not quite as good as slowly reducing the DHW reheat as the cylinder approaches DHW setpoint but it works well.

The evohome setup with DHW wasn't available when I tested so might well work with our boilers but I cannot confirm.

You mentioned that Evohome didn’t work smoothly with your boiler because it couldn’t send a DHW setpoint — I’m guessing that was with a boiler designed to expect full OpenTherm control of DHW, rather than external control via zone valve and sensor?

Yes, we interpreted the OT spec literally, the control must manage all boiler delivery temperatures.

Also, if you don’t mind me asking — which boiler model were you testing Evohome with? I’m currently looking at Ideal Vogue Max, Baxi 800 System 2, and Intergas Xclusive, so knowing whether your test boiler was one of those would really help me make sense of the comparison.

This was around 2015 and HW sent us a lot of kit, they didn't realise the problem of DHW control themselves. Test was with long gone models but I've tested it with all our subsequent boilers and nothing has changed so the current Pinnacle and Synergy boilers will have the same implementation. I have had it at home on the Linea One and now on my Unica Max, at a neighbours property on a Vision Plus and Unica i.

I was also really interested in your comment about flow, return, flue temps, modulation, pressure, and fault codes being available. Were you seeing those via an OpenTherm Gateway or Home Assistant/Homey, or were those values exposed directly through the boiler or Evohome? I’m curious how much of that data is actually exposed when Evohome is used vs. what needs a more advanced monitoring setup.

No, that information is available on our OT room control or app as well as the boiler although I do have pics of the OT monitor presenting performance. Interesting point, our new boiler has lots of information previous models have not offered, modulation for DHW, modulation for space heating, gas valve cycles, hours heating ON etc. I don't actually know whether any of this info will now be available on the control, our training centre is being refurbished and I have no boilers here but OT can definitely supply it if requested by the control. Candidly I'm not sure many would use this and if they did they'd be in front of the boiler anyway.

Finally, on your weather compensation test — that was fascinating. Were you using the boiler’s own outdoor sensor, or was it integrated through OpenTherm? I’ve read some boilers prioritise their internal WC logic over OpenTherm setpoints when both are active, so would love to know how yours behaved.

Er, I'm a bit of a nerd so I used both, a physical sensor and also with the sensor disconnected and the external temperature downloaded though our control. Ours prioritised the boiler sensor when physically connected and applied the room control readings to it. Our OT control had a seemingly more sophisticated WC curve and the boiler a more linear slope. When it was time controlled on OT I found it perfectly adequate but was conscious of the changes in room levels whereas with the less sophisticated boiler WC alone it was simply unnoticeable.

I tested many other permutations, each over 48 hours and adjusted with degree day data. I have no issues with evohome but KISS for me which is also much cheaper although I could have got hold of evohome.

The WC needs two temperatures, comfort and setback if a combi. For a system I would use any OT boiler you choose and EPH.

Thanks again — this kind of insight is gold when trying to spec the right boiler/controller combination.

Don't overthink things, comfort will be fine whatever and 1% on a thousand pound annual space heating bill is a tenner spread over 52 weeks./ Boiler modulation and install quality is key.