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Central heating not being triggered by control panel

Discussion in 'Plumbing and Central Heating' started by Benillsley, 30 Oct 2019.

  1. Benillsley

    Benillsley

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    Hi, I hoping someone may be able to help!
    I have the following system:

    Worcester 15ri boiler
    Drayton RTS1 thermostat
    Drayton Lp522 programmer
    BGMVSP-23 actuator/ mid position valve

    Both the HW and CH have worked fine and independently up until yesterday evening.. Now the HW works fine, turns on as it should and fires up the boiler and I have hot water. However if I turn the HW off and just turn the CH on the boiler doesn’t fire up.

    So far I have checked the mid position valve. By default it’s in the M position in the middle, with both the CH and HW on it stays there as I understand it should?
    With just HW on it moves to W and I have hot water (and the boiler fires up), with just CH on it stays on M when it should go to H? And as previously mentioned the boiler doesn’t fire up and nor does the pump.
    I’ve removed the actuator head and can easily move the valve spindle with my fingers, it only moves about 20 degrees which I’ve read is about right.

    I’ve checked the thermostat is working by removing the cover and jumping the live wire to pin 3 ‘call for heat’. This makes no difference so I’m happy the stat is not at fault.

    I’m not sure where to turn next? Has the programmer just died over night, it actually stopped working as we were changing the timings for the colder weather but this seems to be a coincidence.

    Any advice would be greatly appreciated!
    Thanks
    Ben
     
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  3. ericmark

    ericmark

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    Some thing seems wrong. By default the valve show be in DHW position, i.e. not moved, the white wire is central heating wire and when live the valve should move either to centre if grey wire not live, or all the way if grey wire live.

    There is no supply to valve for hot water, the supply to valve on grey wire is when you don't want hot water. So if there was no connection at all to the motorised valve DHW will still work.

    So a faulty thermostat on the DHW tank would mean DHW will not turn off.
     
  4. CBW

    CBW

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    If it was working as it should and it doesn’t go all the way to the heating side when called for, I would suspect the actuator and not wiring. I take it ch works if you call for both?
     
  5. Benillsley

    Benillsley

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    The valve is definitely in the mid position with the HW and CH off. Turn heating on and it doesn’t move, turn water on and it goes to W
     
  6. Benillsley

    Benillsley

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    Yes CH works when i call for both.. The boiler and pump just won’t fire when CH is requested by itself.
    What tells the boiler to fire up? I assume the programmer and room stat, then the boiler and actuator/valve react? Or am I misunderstanding?
     
  7. ianmcd

    ianmcd

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    Because the HW off is not wired correctly
     
  8. CBW

    CBW

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    Programmer - ch on - room stat calling - motorised valve activates a microswitch inside and sends signal to boiler to fire up. Looks like the more experienced @ianmcd has told you what part of your fault is - he knows his stuff ;)
     
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  9. Benillsley

    Benillsley

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    Whilst it may not be wired correctly it all worked fine before a couple of nights ago something has changed. I’ll look at getting to wired right once I’ve overcome this hurdle!
     
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  11. ericmark

    ericmark

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    There are two ways to power boiler, the tank thermostat is normally a change over switch, the normal open contact feeds boiler, and the normally closed tells the valve to travel all the way.

    The other supply to boiler is the orange wire from the valve. This mid-position-valve.jpg is how the valve is wired, then the central heating runs white becomes live, this motors the valve to centre position at which point orange becomes live that runs the boiler.

    This Y-Plan.jpg is the standard Y plan, note power is required on grey to turn domestic hot water off, John Ward does some good videos on U-Tube Part 1 Part 2 Part 3 it does seem something is wrong, although I would not say wiring was wrong. I have only had to work it out once, and it did not test out as expected as with diodes and resistors you can get some odd readings with a meter.

    I found the micro switch had failed in the valve, and previous owners had latched the valve to bleed position (centre) which got the heating working, although in summer the radiators got a little warm when domestic hot water was called for, my son in law had tidied up airing cupboard and caught the lever which then went to normal resting position, and daughter had no central heating, had to swap whole valve as Sunday and only screwfix open could not buy head or V3 micro switch.

    Looking at the circuit diagram there is no way to explain what happened, however circuit diagram shows two switches, and valve I opened had three, so there must be a few variations, so I would not jump in and claim incorrectly wired as they does seem to have some odd faults when micro switches stick.
     
  12. Benillsley

    Benillsley

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    Ok so I got this bit wrong, the valve is on H when HW and CH are off on the programmer. With HW turned on it stays on H with HW and CH on it goes to the middle (M) and with just CH on it stays in on M but the boiler turns off.
     
  13. ianmcd

    ianmcd

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    post a pic of the wiring of your programmer, when the programmer is set to CH only the valve should motor to H, and then the microswitch will power the boiler, but you need a HW off signal for this to happen, so either your programmer is not switching the HW off terminal or more likely it has never been wired in and that is why the valve was latched in the first place
     
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  14. ianmcd

    ianmcd

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    while the CH and HW are both demanded and the HW thermostat is calling for heat then it will work fine, but when the HW demand is switched off,or the HW thermostat is satisfied , if the HW off switch is not wired in correctly you will get exactly the situation that you have
     
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  15. Benillsley

    Benillsley

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    I’ll post an image when I get home tonight.
    Thanks everyone for the help so far, I’m keen to get it sorted for my cold pregnant wife ASAP!
     
  16. stem

    stem

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    Failure of a microswitch inside the 3-Port valve would cause these symptoms.

    When hot water is required, the hot water cylinder thermostat fires the boiler. When heating only is required (ie the hot water cylinder thermostat has switched off) the motorised valve moves to the heating only position where it operates a microswitch, (SW2 in the diagram posted by ericmark) this microswitch operates and fires the boiler. If the microswitch has failed the motorised valve will be in the correct position, but the boiler won't fire.

    If you have a multimeter and can use it safely, it's fairly easy to check.

    With the hot water 'off' and the heating 'on' check that the valve has moved to the heating only position. If it has, with a multimeter check that the orange wire from the motorised valve is live. If it's not, the microswitch has failed and a new valve, or replacement head is required.
     
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  17. Benillsley

    Benillsley

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    Thank you.
    It’s sounds like, as others have suggested, I have a couple of issues. Firstly with the originally wiring as the motorised valve never goes to H.

    CH on - valve on M
    HW on - valve on W
    Both on - valve on M
    May have been wired wrong from day dot, we only moved to this house in April.

    Secondly,
    Maybe the micro switch has recently failed causing the issue I’m now having. I’ll test the actuator head later (I actually have a replacement on order)
     
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