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potterton profile 80e problem

Discussion in 'Plumbing and Central Heating' started by dexion7, 1 Aug 2011.

  1. dexion7

    dexion7

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    gas turned off
     
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  3. dexion7

    dexion7

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    thought i'd let you know what the problem was: the main gas valve was leaking intermitently and the HT cable was cracked and shorting out thus preventing a spark.

    when heat was called for the pilot valve was opening correctly but as there was no spark it was not lighting. the tow valves are in series and as the main gas valve was passing through, gas was flowing through to the burner but not lighting (the meter needle could be seen moving and you could smell gas).

    whilst we were testing it, the main gas valve did not always leak - it was intermittent. we established this by permanently energising the pilot with 240v and watching what was happening. sometimes the main valve sealed and others it leaked. sometimes energising the main valve meant it sealed again afterwards.

    new gas valve fitted (white rodgers)

    so two faults which resulted in a very dangerous situation. the cracked and damaged ht cable would likely have been fixed had the boiler been serviced.
     
  4. Agile

    Agile

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    I think that you are missing the point of how your boiler works and you may STILL have a serious fault!

    The PCB first opens ONLY the first stage of the gas valve which supplies the pilot burner.

    If a flame is detected at the pilot burner, and ONLY then, it opens the second stage which powers the main burner.

    Please disconnect the HT lead at the PCB or short it to chassis so that there is no spark in the boiler and see if the main burner solenoid is opened. You can see if its opened because the gas meter dial with turn. If so then imediately turn off the boiler/gas as you have a serious fault.

    Then call an RGI.

    Tony
     
  5. dexion7

    dexion7

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    thanks Tony but i'm fully aware of how the pcb works and its interaction with the valves - as is my pal who is rgi fella. i wonder if you read my previous post properly as it clearly explains the sequence of events and faults.

    i dont understand why you consider either he or i dont comprehend the correct sequence of events to create correct main burner operation - would you care to clarify what gave you concern from my previous post?
     
  6. Agile

    Agile

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    Quite simply because you apparently dont understand how the PCB controls the ignition process ( even though I have explained it for you ).

    In respect of the original fault, what tests have you made to ensure that the PCB was not ( wrongly ) powering the main burner solenoid?

    Tony
     
  7. dexion7

    dexion7

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    Well I had no reason to ever understand it or care about it before the problems started but I now have a detailed understanding including a circuit diagram. I replaced the three electrolytic capacitors and reflowed the solder joints on the board connectors whilst it was out.

    I'm clear on how the rectification within the valve connector block in the presence of a flame results in a small dc voltage ( the ac voltage which is present across electode and the pilot finds it easier to flow one way as there is a greater mass of metal in the pilot). The resulting dc small signal is amplified by the transistors on the board and then switches the relay to operate the main valve. In fact despite your comments it may be that my grasp of the theory exceeds your own.

    As regards testing the instalation to establish the fault, As a diyer It was still clear to me that the fault was in the gas valve because the simple test of sitting a test meter across the three terminals on the gas valve showed that there was no 240v on the main gas valve yet even though the gas meter showed that gas was flowing
     
  8. Agile

    Agile

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    I doubt it !

    Particularly if you can see any logic in the highlighted part of what you said above.

    However, if you tested the voltage across the main solenoid while it was passing then I can be relaxed that you dont ( now ? ) have any other problem.

    Tony
     
  9. dexion7

    dexion7

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    well ok it should have said simply 'hotter on the electrode' rather than 'greater mass of metal' but thats just because i'mon the train and not concentrating but i think you're just being pedantic as the rest of the explanation was correct and easily adequate to convince you that i understood the sequence.
     
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  11. monoxide62

    monoxide62

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    Thought those white rogers were now obsolete? , got no coice now but to use the honeywell. :confused:
     
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  12. Agile

    Agile

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    I am not easily convinced.

    Although a hot electrode does cause more current thats not an essential part of the process and it still works fine with a cold electrode.

    The actual rectifying process is caused by the larger landing area of the burner compared to the electrode. Not the mass as such. It can be very thin indeed.

    Tony
     
  13. Agile

    Agile

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    I think they are still available as a grey market direct from the gas valve makers rather than as a boiler spare.
     
  14. dexion7

    dexion7

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  15. gasafengineer

    gasafengineer

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    I can see where the OP is coming from here & don't doubt his word.......................seems to me that the main gas valve was letting by (seating) which wouldn't be an issue if pilot solinoid was shut , once power was supplied to pilot solinoid it would allow gas past main gas valve & into burner , this being the case i would imagine explosive ignition to be the case , good job ignition lead was faulty.
     
  16. gasafengineer

    gasafengineer

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    Spat my tea all over the keyboard. :LOL: , he has a point Agile. :mrgreen: , do you know the working principle behind a MFGV? , seems a grey area to yourself & Monoxide. :p

    Heaven help the Clown Chamber.
     
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