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Oil Boiler keeps turning on mystery... (DDC420 controller)?

Discussion in 'Plumbing and Central Heating' started by Michae1m, 18 Apr 2020.

  1. Michae1m

    Michae1m

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    Hi,

    We've relatively recently bought a house with a DDC420 controller and are struggling to understand some of it's behaviour and wondered if anyone could help. The main problem at the moment is that the boilers seem to fire even when there shouldn't be any demand on them. An example from today, we've had the system on frost mode override to try and have things off but we still keep seeing the boilers running and you can see from the flow temp graph attached that it keeps turning on to keep the flow temp at target despite no demand for hot water or heating (system in frost mode and it isn't anywhere near freezing).

    It feels like we are wasting a lot of oil, we've ended up turning off a lot of the 'smart' adaptive features to try and figure out what is going on (there are other mystery behaviours...) and then possibly build up back from there but the first priority is to figure out how not to waste oil when there is no demand at all... Could this be something wrong with the boiler and not the controller? Sometimes (like in this afternoon for the graph attached) when the boiler is on the boiler section of the web-controls doesn’t show either boiler as 'green' which I interpret to mean the controller is not currently asking for a boiler to fire.







    Any help or suggestions very gratefully received.

    Cheers

    Michael
     
  2. ReJect

    ReJect

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    Any motorised valves (zone valves) on system?
    The actuator heads on them fail or occasionally valve spindle can seize.
    They are most common fault and put live link through their micro switch to boiler. (Grey and Orange wires)
    Needs somebody competent in electrics to test wiring using a multimeter
     
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  4. Michae1m

    Michae1m

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    Interesting, thanks.

    There are a number of zone valves - it’s quite a complex system. There are the upstairs & downstairs heating loops, downstairs is also split into radiators and underfloor heating zones with heatmiser manifolds. The hot water system has two hot water tanks each with a zone valve controlling flow through the tank heat exchanger.
    I’d previously assumed the zone valves were independent of the boiler firing - ie the controller system would fire the boiler based on the space sensor/timer/hot water timer etc and the zone valves would just determine where that hot water would go. I’ve not observed any correlation between the zones being cold and thus opening the valve and the boiler coming on like that but it could happen and without the pumps/vt valve being activated the zone valve opening probably wouldn’t do a lot so we might only notice the boiler coming on but not much else... hmmm - I can definitely trace the wiring though and see if the zone valves do actually have any direct association with the boilers themselves or not.

    The downstairs zone valve has been a bit flaky so that could be a sign...

    Thanks for the suggestions
     
  5. BoilerBob

    BoilerBob

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    If the valve sticks it keeps the circulator running and when the temp on the boiler is low it fires up. Bob
     
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