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CM927: heating coming on even when temperature above what set - or when off

Discussion in 'Plumbing and Central Heating' started by MIKE CROOM, 21 Oct 2021.

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  1. MIKE CROOM

    MIKE CROOM

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    Have seen a fair number of questions about the CM927

    Mine is from a house which we bought in February. And all was well.

    Since putting the heating back on I have had:
    1. Heating coming on in middle of night when set to 6 deg
    2. Heating coming on in middle of day when thermostat temp is several degrees over target temperature
    3. Even setting to OFF - boiler is still on.
    I think I have got rid of problem 1 by making Program Step 1 (of 6) very low and avoiding issues with the Optimisation feature

    But 2 and 3 still an issue. Is it possible the heating is on when there is demand on the water.

    Any troubleshooting steps you can recommend please?
    I'd call the plumber but I can't see a pattern yet and no point in him watching it all working.

    Mike
     
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  3. lloyda

    lloyda

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    When the heating is on when you are not expecting it, what is the light on the relay box doing?

    I always found the optimisation of the cm927 very good. Not sure why you would want to disable it.
     
  4. CBW

    CBW

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    You’ve mentioned the thermostat, but nothing about what type of system you have. Combi boiler with/without zone valves, open vented, sealed system, zone valve(s) or mid position motorised valve?
     
  5. MIKE CROOM

    MIKE CROOM

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    Thank you. This morning the thermostat is on 18.5 with target temp of 16. Boiler on, rads hot (not just warm) No lights on relay unit
     
  6. MIKE CROOM

    MIKE CROOM

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    Thank you. It is an oil combi boiler: Worcester Greenstar Heatslave. Sorry but I don't know the answers about valves.
     
  7. lloyda

    lloyda

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    If there are no lights on the relay it suggests that the thermostat is not calling for heat, and something else is causing the boiler to be on.

    When you find it on when it is not supposed to be, how do you turn it off?
     
  8. MIKE CROOM

    MIKE CROOM

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    I can't turn it off. It goes by itself.
    is it possible that it is demand for hot water but somehow the heat is going to the rads?
    I might experiment more with that hypothesis and call the specialist in.

    Mike
     
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