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Boiler firing even though zones all off

Discussion in 'Plumbing and Central Heating' started by Deansplit, 9 Dec 2019.

  1. Deansplit

    Deansplit

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    I have a closed heating system with 6 motorised valves to zone the rooms/areas plus a heat leak (two 1” vertical pipes are joined by 15mm pipes). I noticed recently boiler continually firing up for a minute or so even though all zones had reached temperature and to double check I turned all zones off and it still happened. So sounds like the boiler is just heating the water in the heat leak - is this a fault with the pump ie. it’s not switching off therefore as soon as the heat leak water cools it fires the boiler?

    Thanks for any advice
     
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  3. fezster

    fezster

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    If your boiler is fired by the SL (orange wire in honeywell 2 port valves) in the motorised valves, it's possible one of the microswitches is sticking. This is quite a common fault.
     
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  4. Deansplit

    Deansplit

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    Thanks Fezster - so how do I check this? Would that not mean the valve at fault would be stuck on open so therefore the rads are always on (which they're not)?
     
  5. imiller9

    imiller9

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    No, the valves have a permanent 240v feed to them and if the switch is stuck it will pass that voltage onto your boiler without the valve to physically open.
     
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  6. fezster

    fezster

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    It's easy to check with a multimeter and access to the wiring centre.

    However, if you're not confident in doing so (as there will be live electricity flowing when doing the check) then better to call somebody in.
     
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  7. Deansplit

    Deansplit

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    This is fine, have done lots of wiring in the past and have a very good multimeter. But is it easy enough to explain exactly how I go about checking? The pump is constantly on and very hot unless I physically switch the boiler off so I presume I need to sort this ASAP for fear of damaging the pump?
     
  8. ianmcd

    ianmcd

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    inside the wiring center there will be a grey wire for each valve all connected together, these have a permanent live connected, there will be an orange for each valve and these will all be connected and will be connected to the switched live at the boiler, with everything switched to off (not the fused spur) test for live at the terminal with the orange wires, if there is live there, you need to turn off the power and seperate all the orange wires and test for continuity one at a time with the grey wires, when you find which one has continuity trace that one to which valve it is from and change the actuator
     
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  9. fezster

    fezster

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    Just to add to ianmcd's comprehensive post above, you may find if you activate and deactivate the microswitch a few times, it becomes unstuck (assuming that is the fault). Might be worth trying before ordering a new actuator.
     
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  11. Deansplit

    Deansplit

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    Thanks but this would surely mean the rads of that zone would be getting heat?
     
  12. ianmcd

    ianmcd

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    No, you misunderstand how the valve works, when asked to heat the zone, the valve motor is powered, this opens the valve to allow the flow of water to that zone, once the valve is fully open, this makes the micro switch , this tells the boiler and pump to operate, when that zone is satisfied the power to the motor is stopped so the spring return mechanism closes the valve, then the micro switch should go open circuit and stop the boiler from firing, but the switch is sticking but the valve is closing, so the boiler still fires but the valve is closed so the heat has no where to go so the boiler gets hot too quickly and shuts down, then cools and starts heating again
     
  13. Deansplit

    Deansplit

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    OK thanks for the detailed explanation, that helps :) Soooo, is the faulty one's switch is now on forever (or until freed up or replaced) or if I switch the fused spur off, will it reset, in which case, if it does I could test each MV one by one by switching it on and seeing how the boiler runs? Think you're going to say no, but just though of an easy way to check if this is the case.
     
  14. ianmcd

    ianmcd

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    I have already told you how to test it, not rocket science, if you are unable to do that it is time to get someone in
     
  15. Deansplit

    Deansplit

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    Yes, and in theory that's easy to test but as you can see, it's not as clear as you've described...
     

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  16. ianmcd

    ianmcd

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    yes it is , turn the power off and pull everything out and spread all the connections
     
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  17. Deansplit

    Deansplit

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    Sorted this today :) And delighted that when I took it apart rather than just buying a new one, that I saw lots of plastic had worn off to the metal ring which has the cogs on... scraped this off and bingo, works a treat ;)
     
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