Apollo CH and Overheat Stat and TC

Discussion in 'Plumbing and Central Heating' started by Pacman, 30 Sep 2006.

  1. Pacman

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    Following on from other thread had the boiler (Thorn Apollo 15/30) serviced and the TC changed and the Oheat stat replaced, the guy changed some 'A' clips so that the cowl pulled tight against the back as the old clips were threaded and all seemed well the boiler fired up and we have had heat and HW for 2 days now.

    BUT

    Now the boiler won't light AGAIN it's gone out and won't relight, now it seems the Oheat stat is gone again but I don't want to keep calling someone back to just change it so it works for a day and pops again.

    Why would the Oheat stat keep going? is it meant to fail safe or is it meant to cool down and reset? or is there something else?

    The Stat he replaced was on the left hand side above the TC and buts up against the heat exchanger, he didn't change the Low stat where is this? should it need changing?
     
  2. Agile

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    That model is a low water content and is very sensitive to the flow rate and will overheat if TRVs close and you have no system bypass.

    I thought the overheat stat was in series with the thermocouple and once it had cooled down the pilot will relight?

    Tony
     
  3. Gasguru

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    Don't assume it may be overheating there are other reasons for pilot outage. Sometimes once overheat stats have opened despite cooling and closing the pilot can be difficult to light.

    Unfortunately there are many reasons for the pilot to go out.
    Get the installer back and start by checking the following:

    Pilot not blocked (crisp blue flame)

    Pilot adjusted correctly.

    Genuine TC and o/heat stat used

    Top socket not split/corroded

    Pilot shield in place

    Pilot sight glass not cracked/seals OK

    Casings seals OK

    Casing correctly fitted especially around TC/pilot supply pipework

    Heat exchanger not blocked (very common - and can take an hour to clean out)

    Blocked gas valve inlet filter

    Flue not corroded

    Flue outer cover plate not missing

    Flue not in a high wind position

    High thermostat working correctly

    Bypass pipework

    Bypass adjustment

    Pump not running slow/ impeler not blocked

    Pump overrun operating correctly

    Blockages/poor water circulation

    Incorrect or faulty wiring

    and probably several other items..........



    Sometimes it can take a few visits - just start with the simplest and cheapest problems to solve.
     
  4. Pacman

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    Does a high stat fail safe buy being closed circuit or a open circuit?
     
  5. Gasguru

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    The high stat goes open circuit once the flow pipe water hits around 80 centigrade, this then turns off the gas valve solenoid. Putting the thermostat switch on low switches in the low stat that probably opens up at 60 or 65 centigrade.

    These stats have nothing to do with getting the pilot to light.

    When is the service engineer coming back?
     
  6. corgiman

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    soundfs to me like a circulation problem
     
  7. Pacman

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    Got the guy back to have a look, he simply bent the TC more into the pilot light and now its holding, all working good now. :D

    I'm selling the house soon and would like to have the boiler certified as safe before i sell, what should I expect from a engineer to certify as safe i.e. is a service record enough or is there a scheme?

    Also when I look up a Corgi engineer on their website it gives me 10 or 12 within a couple of miles what's the best way of picking one or can anyone recomend an engineer around the Gatwick area

    Cheers :D
     
  8. Gasguru

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    Bending a TC is not a standard procedure. On universal types the intrusion into the flame can be adjusted a little on the thread.

    Are you trying to tell us he wasn't corgi registered. Otherwise why didn't
    you get him to issue a gas safety record whilst he was there. A registered engineer has a legal responsibilty to ensure the boiler is safe and operating correctly and these safety checks are mandatory.

    I hope the heat exchanger was checked as they are renowned for becoming blocked and are a pain to clean. Its a dead givaway for highlighting lack of proper servicing.
     
  9. Pacman

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    Coming back in the week to complete the task, just want to know what to expect like the gas safety record you mentioned,

    heat exchanger is a ok
     
  10. Agile

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    As explained there is no significant adjustment on the thermocouple but the pilot can be adjusted to better illuminate the thermocouple.

    The standard arrangement on your boiler has a very large pilot flame which never normally gives any illumination problems.

    On the original thermocouple on that boiler the over heat stat has screwed connections to connect to terminals on the thermocouple lead. The usual method now is 6 mm spade connectors.

    The list avobe missed out checking that any screwed connectors are tight and the connection surfaces are clean. A little crocus paper will help.

    An assessment of any problems can be made by measuring the thermocouple output voltage on each of the interruptor tags.

    Tony
     

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