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Baxi Combi 80E - no hot water

Discussion in 'Plumbing and Central Heating' started by ChasW1, 23 Feb 2009.

  1. ChasW1

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    Hi. Help please. Central heating ok but no hot water. On h/w mode the pump runs but can't hear the boiler fan and burner does not light. No fault lights showing just the green light to confirm h/w mode. Water pressure and flow is fine. The pins on the diverter valves pop out ok and as far as I can see the microswitches ok. have tried over riding them by connecting the wires together but this makes no difference. Am I right in assuming that the pcb is faulty? If I take off the temp sensor wires the panel shows them as faulty so I am assuming they are ok
     
  2. Agile

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    On top of the diverter valve there is a smaller pin which operates a switch when there is flow round the system.

    You will probably find the pin is not reliably operating the switch in the DHW mode.

    Check and to test activate the switch manually.

    Tony
     
  3. ChasW1

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    Hi. Thanks for suggestion. The pins on both diverters work ok and have tried activating both manually. The one on the top works ok on CH mode and the one on the side works on DHW mode. Have tried manually operating CH mode switch when running DHW only and makes no difference
     
  4. Agile

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    The one on the top is NOT a CH switch!

    It is a system flow switch and has to operate in either mode before the boiler is allowed to proceed to ignite the gas.

    If the top one really is operating on CH, then I agree that it may be the PCB but it would be better if you first accept what I have advised you and then recheck the system switch before you consider spending about £100 on a new PCB.

    Tony
     
  5. ChasW1

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    Hi Tony. Thanks for reply. Have tried a bypass on flow switch when in DHW mode and it has no effect. If I run both DHW & CH with bypass still in place it does not run. However, if I then shut off DHW flow the DHW piston retracts and CH runs. As soon as I reinstate the flow the DHW actuator piston moves out, the microswitch kicks in and it cuts the gas and the fan. As soon as I stop the flow the piston retreats and CH back on. I have also tried a similar bypass on the DHW switch. I assume its not the temp sensor as no fault lights show until I disconnect the actual sensor itself. Diff to check out as don't have a meter.

    Charles
     
  6. Agile

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    I think that your description may be a little confused because talking of just a "flow switch" can mean anything.

    Your fault seems to be either the DHW flow switch, the PCB or the DHW sensor is low resistance. Thats last unusual but keeps the gas off because it thinks its hot enough!

    You can substitute a 10k resistor for the DHW sensor.

    OR

    Get a simple test meter! Its not really possibly to fix a boiler without one.

    There is also a strong possibility that the DHW flow switch has failed! Its a change over switch and it may not be operating fully!

    Tony
     
  7. ChasW1

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    Hi Tony

    Thought I would let you know the outcome. I ordered a PCB and DHW sensor. It turned out to be just the sensor. Anyway I decided that I may as well replace the board as I had bought it. So did that today & would you believe that that the boiler would not run!! The first two neons on the display were flashing. So put the old board back in and all was well. Presume so called new board faulty.

    Many thanks for your help

    Charles
     
  8. namsag

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    When new board fitted you have to hold it at reset position for 3 seconds , sometimes more than once.
     
  9. ChasW1

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    Hi. Thanks for that. I did try a reset but in view of what you advise I will pop the board back in & try again.
     
  10. Agile

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    A £15 test meter would probably have saved you the cost of the PCB !

    Tony
     

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