2 BDR91's in parallel?

[John Bennett]

I’ve re-graded my heating system to evohome, works fine at present. There are numerous HR92 controlled radiators plus a single radiator in a separate room that is always live, ie. no thermostat fitted. After fitting evohome, I have a redundant CMS927 controller with its own BDR91. In essence, this controller could be used to control the temperature in that room!
Can the 2 the BDR91’s be wired to the boiler in parallel using the A and C control terminals? If not, why? Probably not recommended, but has anyone tried and won?

[John Bennett]

Sorry, regarding my question, that should be terminals A and B of the control circuit.

[Richard]

evohome works on a aggregated percentage demand, therefore if you were to use the CM927 in this way you would upset the TPI control of the evohome BDR91 which is inefficient...