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The radiators on the ground floor will be replaced by floor heating and I'm planning to install a Honeywell HCE80 and connect it to my Evohome.
During my research I've found information that the combination R8810 (Opentherm) and Honeywell HCE80 is not ideal.
See article: https://www.scribd.com/doc/114043217/Ev ... T-1120-01#

Best the BDR91 (on/off) should be used instead of the R8810 (Opentherm).

Question:

• Is it possible to use the BDR91 in combination with OTWG, so it's still possible to see what's going on in the boiler?
• Which OTGW-settings should be taken care off?

To be complete my boiler is a Vaillant ecoTEC Plus 30-34/5-5L.

I don't understand the reasoning of the article you reference. The evotouch collects the heat demand of all zones and controls the boiler based on that. If all zone valves are closed, an opentherm controller could still request the boiler to heat. But so could an on/off controller. So how does that make on/off control better?

Or is the on/off controller supposed to be connected in series with a relay contact of the zone valves? So that if all valves are closed, the signal from the thermostat cannot get to the boiler. If that's the case, I guess a new feature could be made for the OTGW that would allow the valves to be connected to a GPIO pin. If all valves are closed, it could switch off the boiler. Similar to CS=5, CH=0, or something along those lines.

I don't understand the configuration well enough to be able to imagine what would be needed. But in any case, it is possible to connect an on/off thermostat to the OTGW and have it still talk opentherm to the boiler. See the (updated) description on the web site. I haven't used that option myself. So I can't really say how well (or poorly) it works in practice.

The setup will be:
* HCE80 on the ground floor with Evohome in the living room
* 5 HR92 on the 1st and 2nd floor
* Opentherm or on/off to control the boiler

According to the article with Opentherm the boiler water could be to low for proper heating the ground floor because the HCE80 is in principle acting as a on/off valve system.

I've read your section about the On/Off thermostat connected to the gateway and this could give me the option of both using the BDR91 as well as still getting information about the status of the boiler.

I was thinking of telling the boiler the set the max water temperature to E.g. 50 degrees. What is in your opinion the best way to do this?
Via a command in the gateway? This because I expect the boiler setting will be overruled by the command send by the gateway

Hi Schelte,

Thanks for your answer. I've have given it a second thought and for now I will keep my setup with the OpenTherm bridge (R8810).
Like you said it's not to expect that the on/off control will be better.