Gas boiler over-running

Discussion in 'Plumbers' Talk' started by Puffer, Jan 11, 2010.

  1. Puffer

    Puffer Member

    My gas boiler is in a 'side loft' under the eaves of the house, a cold but not freezing location even in current weather. It is controlled by a Honeywell ST7000 programmer (basic but adequate) and there is a Honeywell frost stat fitted just above the boiler. All has worked well enough for some years.

    The programmer is set to switch 'off' at 10.30pm but on several nights recently the boiler has continued to run. The programmer is not then showing 'on' and, to turn the boiler off, I have to use the override button twice to show 'on' and then 'off'. The overrun has not occurred at the morning switch off time.

    I am very doubtful that the cold weather is triggering the frost stat - and why should it when the boiler/system has been running for several hours? But, if the frost stat is operating, surely I would then be unable to switch off using the override? Perhaps the programmer is faulty (sticking relay?). Any pointers would be appreciated so I can investigate further.

    There is no pipe stat on the return (in series with the frost stat) and maybe I should fit one - but that has no bearing on my present fault, does it?
  2. Puffer

    Puffer Member

    Surprised that no-one has yet commented - but I guess you are all busy. Any ideas from anyone gratefully received.
  3. GT Sutty

    GT Sutty New Member

    Sorry I do not have an answer to your query but I find it interesting that all the people who like to give smart answers to the normal questions are suprisingly quiet.
  4. Puffer

    Puffer Member

    Yes indeed, GTS. But I've a feeling that the smart (but not in the sense of intelligent) answers may now just start because you and I have prodded. Ho hum.
  5. Mr Kipling

    Mr Kipling New Member

    You say you have no pipe stat on the return then that could be your problem.
    If the frost stat says "its cold outside, lets fire the boiler up to stop it freezing", you need the return stat to say "it's OK now, the water in the boiler is toasty and you can switch off"

    You see ?
  6. Puffer

    Puffer Member

    Understood perfectly, Mr K, but I don't think so: (a) never had this problem before, even in very cold weather; (b) area around boiler nothing like freezing when it has been running for some hours - so why should frost stat think it's cold and call for heat, so overriding timeclock?

    I do agree that pipe stat advisable to ensure switch off, as you describe. I shall fit one in due course, prob a Siemens RAM1.T (which suits cylinders or pipes), and set it to 20-25 deg.

    I tested frost stat yesterday; live feed OK but it wouldn't 'make' even when turned up from normal 5 deg setting to max 20 - it simply wasn't cold enough. When boiler fired manually, reverse feed to stat showed external wiring OK.

    I do think programmer relay is simply sticking 'on' sporadically but further comment welcome.
  7. Dick Puller

    Dick Puller New Member

    You could be right puffer, your programmer or indeed another heating control may be faulty.

    Your frost stat makes on temperature fall.


    Seems almost too obvious. PROGRAMMER
  9. Tony Soprano

    Tony Soprano New Member

    sometimes we just dont bother answering the simple ones because we cant have go at each other.specially the little scottish git!;)
  10. Puffer

    Puffer Member

    Thanks, folks - we all seem to agree that the fault is in the programmer. As it is intermittent, my bet is that it is mechanical rather than electrical and I will check the relay.

    Sorry not to have provided much material for violent argument, pompous pontification, sarcasm, insults, etc. Next time, maybe ...
  11. Dick Puller

    Dick Puller New Member

    the little scottish git........Yeah, he's not been on here for some time??

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