Help with Evohome / Opentherm / Intergas

[paulockenden]

What isn't normal (for me) under OpenTherm is persistant demand at full CH output for 'topping-up' lost heat where a lower flame height would suffice.

Don't forget that the proportional band is only 1.5 degrees. Any zone further out than that and the boiler will be going full-pelt.

Maybe the band needs to be wider when under OpenTherm control?

[fergie]

Is it possible but under OT the boilers are *supposed* to surrender full control, but the Atag (which I deliberately went for) valiant simply don't?

Under one zone the evohome acts like a normal controller and only calls for x about of heat, but under multizones it maybe calls for x+y which is more than the safe limits? If that were the case though, surely the fix would be a software update in evohome so that multizone gives the same signal as single zone?

Like Hengas, I haven't had a winter with my boiler yet, but when I watch water only it seems to gradually build up- not go full pelt from the go. Again with a heat demand it seems to build in s controlled manner. I guess I won't know for sure though until winter and there is a call for heat from 10 rooms at once.

[HenGus]

Clearly, the one thing that is a given is Evohome. The variables that lead to varying outcomes are different boilers and interfaces. At this point, I declare an almost complete lack of detailed technical knowledge; however, a simple read of the OT/OT+ specification shows that all the parameters (IDs) passed from controller to boiler are not mandatory. Logic would suggest that if Evohome demands 90C for DHW heating, and the boiler spends back an 'invalid ID' response then the boiler will just do its own thing based on the set profile and user settings. Out of interest, has anyone found the Opentherm logo on any Evohome device or interface? Come to think of it, my boiler doesn't show the logo either.

[blowlamp]

Clearly, the one thing that is a given is Evohome. The variables that lead to varying outcomes are different boilers and interfaces. At this point, I declare an almost complete lack of detailed technical knowledge; however, a simple read of the OT/OT+ specification shows that all the parameters (IDs) passed from controller to boiler are not mandatory. Logic would suggest that if Evohome demands 90C for DHW heating, and the boiler spends back an 'invalid ID' response then the boiler will just do its own thing based on the set profile and user settings. Out of interest, has anyone found the Opentherm logo on any Evohome device or interface? Come to think of it, my boiler doesn't show the logo either.

Not Evohome, but from the Remeha manual.

Capture.JPG

[HenGus]

Getting back to Evohome and Opentherm. There is a recent comment on the Domoticz forum:

Thanks for raising the issue of the OT module. I really need to update the wiki to list Evohome devices which are only partially implemented. The code still doesn't really handle the OT module correctly and gets confused by all the different boiler demand messages and you end up with multiple boiler relays.

Might this explain the Intergas/Opentherm issue?

[paulockenden]

Might this explain the Intergas/Opentherm issue?

Doubt it - this is talking about traffic from the other side of the bridge.

P.

[dty]

Getting back to Evohome and Opentherm. There is a recent comment on the Domoticz forum:

Thanks for raising the issue of the OT module. I really need to update the wiki to list Evohome devices which are only partially implemented. The code still doesn't really handle the OT module correctly and gets confused by all the different boiler demand messages and you end up with multiple boiler relays.

Might this explain the Intergas/Opentherm issue?

As Paul says, that's nothing to do with the boiler. That's Domoticz understanding the OT messages produced by the HGI80.

DanD and I are still working (very slowing) in the background on that. I think Dan is waiting for me to capture him some OT messages which I can't right now because none of the custom firmware for non-HGI devices (including my firmware) can cope with the messages - there's something slightly different about them that I need to explore.

But again, that thread is talking about the radio messages between the controller and the OT bridge.

[HenGus]

As Paul says, that's nothing to do with the boiler. That's Domoticz understanding the OT messages produced by the HGI80.

DanD and I are still working (very slowing) in the background on that. I think Dan is waiting for me to capture him some OT messages which I can't right now because none of the custom firmware for non-HGI devices (including my firmware) can cope with the messages - there's something slightly different about them that I need to explore.

But again, that thread is talking about the radio messages between the controller and the OT bridge.

Thanks. Excuse my lack of knowledge, but how do the messages produced by the HGI80 differ from the messages produced by the Opentherm Bridge?

[dty]

Thanks. Excuse my lack of knowledge, but how do the messages produced by the HGI80 differ from the messages produced by the Opentherm Bridge?

Evohome uses a proprietary radio protocol to communicate between all its components. (You know this!)

The OpenTherm Bridge receives instructions and information from the controller and converts it to the OpenTherm protocol to send down the pair of wires to the boiler. Details of the OT protocol are publicly available.

The HGI80 (and similar hackalikes) listens to all the Evohome radio traffic and produces one line of text on its USB port in a particular format for each message received. It needs to understand the physical details of the messages (radio frequency, encoding, etc.), but not what each message means.

Domoticz can read these lines and interpret them into things like zones, temperatures, demand, etc., but since the protocol details are not in the public domain, it takes a dedicated bunch of people like Dan to try and make sense of each line coming out of the HGI80.

[the crooner]

Just to close my input into this thread and to thank folk for the useful information.

We are going to keep the existing boiler until it dies, have installed a megaflow 210 unvented tank and implement a full Evohome system with 11 rads and hot water. Since we obtained the cylinder from clearance I'm not yet sure what type of thermostat pocket it has but whatever I'm sure we can overcome that. Will keep the existing motorised valve and control via Evohome and install the supplied new valve controlled by the existing tank therm/cutout circuitry.

We will get an opentherm boiler when the current one expires. Hopefully by then all the opentherm compatibility issues will be resolved.

Thanks again

Tony