I have had an Evohome kit for a few years and have had no problems with it until we recently had our boiler replaced from a Grant Oil Combi to a new Worcester Greenstar Heatslave II Oil Combi and now it seems like both the boiler and evohome have a mind of their own.

I am noticing that often the BDR91 relay will show a green light and the boiler demand light will be on but the boiler is not firing or sending any heat to the radiators, this can go on for up to an hour or more and causes the room temperature to drop a few degrees below the set temperature. When the boiler does eventually fire the BDR91 sometimes clicks off for a few seconds then back on which seems to make it worse because the boiler then stops again for a long period. The rooms all heat up fine in the mornings and evening it just seems to be a problem maintaining the level.

I have also seen the green relay light come on for a few minutes then go off when the heating should be off i.e all rooms have set points a couple of degrees below room temp.

We have had our installer back and he has thoroughly tested the boiler but doesn’t believe it is at fault. He advised us there was low current from the relay and we have since replaced the relay with a new BDR91 unit but this doesn’t seem to have made any difference.

I have factory reset the controller and this has the default 6 cycle rate and 1 min on time.

I appreciate the description is somewhat non specific but wondered if anyone can advise if any of this seems normal and if not whether this is likely to be the evohome or the boiler causing the issue?

Chris