The Efficient Home Forum

I have recently added the evohome CH (no HW) system to my boiler.

I originally had a Ideal Halo thermostat connected to a Ideal Smart Wiring Centre and Smart Interface with OpenTherm connected to our Ideal Logic Max 30 condensing system boiler.

In order to connect up the BDR (CH only) I connected the BDR91 to the smart wiring centre which will now fire the boiler from either the old or the new thermostat. I did not plan on using the old stat for anything except HW so turned the temps down low enough that it should not need to fire the boiler.

Now this is generally working quite well. The BDR91 is firing the bolier and in the morning most zones are hitting the temperature although perhaps a little slowly. I imagine the system is learning. If I turn a room up manually it tends to heat up in about an 30 mins to an hour depending on the room

However, I have noticed one zone in particular in the afternoon will start optimised heating an hour before but is not hitting the setpoint at the required time. It tends to only gain a few degrees in that hour and be 3 degrees short of the setpoint. Now I will note our house is old and cold and not particualarly well insulated. This radiator/room can be pretty cold in the current month/s generally.

I'm also curious as to the effects of Opentherm in my wiring above. When the BDR91 fires, the smart wiring centre opens the valve, waits for the valve open return signal and then sends a signal to the Ideal Opentherm device to fire the boiler. As I understand it Opentherm would need to know the last required temperature from the thermostat to talk and agree the flow temp with the boiler. As the BDR91 is on/off (not Opentherm) it would I assume not give a temp. Therefore would it use the last or current temperature given by the old Ideal Halo thermostat (which I am not using for CH)?

Can anyone shed any light on this? I'm wondering if the remaining Opentherm connection might be limiting the flow temp and slowing down the heating. I'm thinking it is either that or the room/zone in question needs a bigger radiator or other in nearby zone to assist in hitting the setpoint.

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jimbomcbob wrote:I have recently added the evohome CH (no HW) system to my boiler.

I originally had a Ideal Halo thermostat connected to a Ideal Smart Wiring Centre and Smart Interface with OpenTherm connected to our Ideal Logic Max 30 condensing system boiler.

In order to connect up the BDR (CH only) I connected the BDR91 to the smart wiring centre which will now fire the boiler from either the old or the new thermostat. I did not plan on using the old stat for anything except HW so turned the temps down low enough that it should not need to fire the boiler.

Now this is generally working quite well. The BDR91 is firing the bolier and in the morning most zones are hitting the temperature although perhaps a little slowly. I imagine the system is learning. If I turn a room up manually it tends to heat up in about an 30 mins to an hour depending on the room

However, I have noticed one zone in particular in the afternoon will start optimised heating an hour before but is not hitting the setpoint at the required time. It tends to only gain a few degrees in that hour and be 3 degrees short of the setpoint. Now I will note our house is old and cold and not particualarly well insulated. This radiator/room can be pretty cold in the current month/s generally.

I'm also curious as to the effects of Opentherm in my wiring above. When the BDR91 fires, the smart wiring centre opens the valve, waits for the valve open return signal and then sends a signal to the Ideal Opentherm device to fire the boiler. As I understand it Opentherm would need to know the last required temperature from the thermostat to talk and agree the flow temp with the boiler. As the BDR91 is on/off (not Opentherm) it would I assume not give a temp. Therefore would it use the last or current temperature given by the old Ideal Halo thermostat (which I am not using for CH)?

Can anyone shed any light on this? I'm wondering if the remaining Opentherm connection might be limiting the flow temp and slowing down the heating. I'm thinking it is either that or the room/zone in question needs a bigger radiator or other in nearby zone to assist in hitting the setpoint.

This is a complex situation, so no easy answer here unless someone else has specifically tried this situation (which I haven't).

So from simple testing I can tell the old thermostat is being used with the opentherm calculations with the boiler. If the old stat is set low the boiler goes into low output and if I turn the old stat up it goes to high output.

I have decided it would be best to install the evohome opentherm bridge. My current ideal opentherm device is connected to the boiler OT Master connection. The OT Slave connection is not currently in use. Am I correct in thinking I can connect the evohome opentherm bridge to that free slave connection?

I figure this way both stats will remain connected along with my separate HW. I would swap them but my HW will still be on the old thermostat and I don't wish to replace this with the evohome water kit at this time.