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Rads getting hotter and hotter regardless of thermostat

Discussion in 'Plumbing and Central Heating' started by gregch, 18 Oct 2021.

  1. gregch

    gregch

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    Feeling a bit warm yesterday evening, checked the radiators and they're all fierce hot - checked the wireless thermostat and it was reading 25 deg, and rising, even though it was set to 21 deg.

    The display on the wireless thermostat (Honeywell DT92E) was showing the flame symbol (calling for heat??) and flashing 'radio waves' (communicating with receiver??).

    The programmer was 'on' - ie it was during the programmed time for the heating to be on. Switching the programmer to 'off' turned off the boiler and the rads then cooled down. Have left it switched off for now.

    When this happed a week or so ago, I suspected it might be that the motorised valve actuator had stuck, (that has happened before a couple of years ago) so I replaced the actuator (as I did that previous time) and everything was fine again until last night.

    Oddly enough, when I fitted the replacement actuator I noticed that the lever, which I believe is supposed to return itself to the "Auto" position when unlatched from "Man" actually seemed to stick halfway. Looking at it again now, with everything switched off, the lever is sitting halfway across, whereas the other actuator (for hot water) is parked in "Auto".

    Is it possible that the replacement actuator is faulty, or is it more likely that there's some kind of intermittent issue with the thermostat? (I couldn't understand why the thermostat was still displaying the flame symbol when the temperature was already way above where it was set) (or does the flame symbol display whenever the boiler's firing??)
     
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  3. CBW

    CBW

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    Did you check the spindle when you replaced the actuator?
     
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  4. jackthom

    jackthom

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    The problem is almost certainly with the thermostat. The fact that turning the programmer to OFF halted the heating suggests the the thermostat is communicating ok with the receiver unit at the boiler end so I’m not sure what the problem might be, just that the actuator is simply doing what it has been told by the thermostat.
    That’s assuming the programmer you are referring to is built into the thermostat.
     
    Last edited: 18 Oct 2021
  5. gregch

    gregch

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    Not sure about check it - I did align the flat part of the spindle with the front of the valve per instructions... though the replacement actuator (with lever latched in man position) did need a tiny bit of finessing to fit properly onto the spindle/valve body.
     
  6. ETAF

    ETAF

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    I think this comment shows its the thermostat as it is asking the boiler to heat

    have you changed the batteries , seems like a faulty thermostat
    As its was calling for heat, so the boiler was doing what it has been told to do, by the thermostat to keep heating.

    I would not look anywhere else, until the thermostat when it reaches the required temp setting, actually turns off the request for heat symbol

    I know some one who has recently changed to the Fisher heating and each radiator comes with a wireless thermostat to control each radiator.
    The batteries dont last a year , she is replacing every 4 - 8 mths
     
    Last edited: 18 Oct 2021
  7. gregch

    gregch

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    Ah, no - the programmer is a separate unit - a Horstmann H27XL - and that sets the times that the heating comes on and off. The thermostat just sets the temperature (or used to, at any rate).
     
  8. jackthom

    jackthom

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    Sorry, I missed the bit where you said that with everything switched off the actuator wasn't closing.

    Is that still the case when the power to the boiler (ie the whole system) is switched OFF?

    If it doesn't then the problem is with the actuator.

    If it does close with power OFF does it then also close when the power is on but programmer is set to heating OFF?
     
    Last edited: 18 Oct 2021
  9. gregch

    gregch

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    If the programmer is set to heating OFF, the boiler shuts off and the rads cool down.

    If the programmer is set to heating ON (or is timed to be on), the boiler continues to fire and the rads continue getting hotter, even when the temperature is already higher than what the thermostat is set to.

    What seems especially odd to me is that the thermostat will display eg 25 deg (so it obvs "knows" it's 25 deg), and it's set to eg 20 deg, it still displays the flame symbol as though it's continuing to call for heat.

    What I don't really understand is whether the flame symbol means the thermostat is calling for heat (which would imply a fault with the thermostat), or whether the thermostat somehow 'knows' the boiler is firing because (eg) the actuator is stuck on, and is displaying the flame symbol to indicate that. The instructions Honeywell provide for the DT92 don't make that clear (at least, not to me!).
     
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  11. ETAF

    ETAF

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    the thermostat I had would switch the flame signal on when temperature was required. And with the Boiler Receive box , which had an ON/OFF if i turned that off , the heat symbol was still on from the thermostat - so was certainly a thermostat function on my old one, cant remember the make and model , was installed in my old house around 2012 ish

    Same on the Fischer system, no boiler involved, just electric rads and so the thermostat also the time etc - flame symbol is when the remote thermostat switches the power on

    did you change the batteries as suggested ?
     
  12. gregch

    gregch

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    Have changed the batteries and testing it again right now. Thanks for your help, btw.
     
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  13. gregch

    gregch

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    OK so have tested again and so far it's working correctly. Observing the valve, it seems to operate correctly even though the lever isn't fully returning to the "Auto" position like the HW one does. Unfortunately I have zero confidence the problem is fixed for good, because I've done nothing other than turn the wireless thermostat off and on again! (although I replaced the batteries, according to multimeter the ones in there were fine). This thermostat was only replaced a year or so ago due to its predecessor (identical model) developing a fault with its wireless communications so not great if it is that at fault.
     
  14. ETAF

    ETAF

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    unless the multimeter has a battery test setting, then on no-load batteries can appear fine
     
  15. ericmark

    ericmark

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    If my wall thermostat sticks on, it will cause my boiler to cycle off/on, however my radiators will not over heat, each radiator is controlled by a thermostatic radiator valve (TRV) except for bathroom towel rail, also the boiler has a control for water temperature which limits how hot radiators can get.

    So yes likely the thermostat is faulty this IMGP8037.jpg thermostat went wrong with me, slowly loosing RF link and staying on, but this 84067_P.jpg thermostat has a fail safe, so if no RF in ½ hour it auto closes down. But with gas boilers you don't want the on/off wall thermostat controlling room temperature, it is only there to stop cycling in warm weather, and that thermostat will fail safe also used a mark/space ratio to stop over shooting which means the gas boiler does not run as efficiently, with an oil boiler great, but gas boilers modulate so either a modulating wall thermostat most common is OpenTherm or it uses the TRV to control temperature.
     
  16. Londoner2

    Londoner2

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    I had a theromostat like that, salus T105RF, it was awful, programming was really difficult, it always caused teh boiler to recycle endlessly, replaced with a app/internet based salus it500 and never looked back, much easier to prgramme, visually easy on the eye and stopped the recylcling.
     
  17. gregch

    gregch

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    It's an oil boiler in this case, and a Honeywell DT92 wireless thermostat + relay which actually has never been exactly reliable.
     
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