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  1. #1
    Automated Home Lurker
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    Default Confused about Evohome and new boiler

    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

  2. #2
    Automated Home Legend paulockenden's Avatar
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    “Low current from the really” makes me suspicious that the installer doesn’t have a clue what they are doing.

    It's a relay. A switch. It doesn’t provide power.

  3. #3
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    I have to agree it does seem a bit odd. What I don't understand is, the relay is just a switch so when it is on "green light" the boiler should be sending heat to the rads, if the boiler demand light is on and there is no heat going to the rads for up to a hour at a time then surely this is the boiler at fault?

  4. #4
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    Quote Originally Posted by bluecat View Post
    I have to agree it does seem a bit odd. What I don't understand is, the relay is just a switch so when it is on "green light" the boiler should be sending heat to the rads, if the boiler demand light is on and there is no heat going to the rads for up to a hour at a time then surely this is the boiler at fault?
    It sounds as though it may not be wired correctly and/or there is fault with boiler for the relay connects the circuit, the power goes to the boiler, it fires up. I wonder if the installer is wanting to find an excuse for his failure?

  5. #5
    Automated Home Legend paulockenden's Avatar
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    What's the temperature of the flow/return pipes? If the water is hot then the boiler won't fire.

    Could be something like an airlock preventing the water flow.

    P.

  6. #6
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    I don't know much about oil-fired boilers, but I do know you're not meant to turn them on and off rapidly. Could it be that you need to play with the cycle time and minimum on time in Evohome? Is it trying to modulate the heat too rapidly and the boiler is ignoring it to protect itself? Check the installer manual for the boiler - it might tell you what the maximum number of hourly cycles is.

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