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Vaillant Turbomax plus 824e DHW problem.

Discussion in 'Plumbing and Central Heating' started by whistler, 14 Jul 2020.

  1. whistler

    whistler

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    Boiler is a Vaillant Turbomax plus 824e. Problem is no domestic hot water. CH works fine.

    When hot water tap is opened, no led or status indication on boiler, so not detecting request for hot water. Initial thoughts were a problem with the Aquasensor.

    Struggling to get an engineer out today, waiting for call back so whilst waiting, browsed the web for info and came across a video explaining how to electrically test the aqua sensor. Being an electronics engineer, I checked the wires to the sensor with my meter, but there is no voltage across the three wires. Video shows 4.6v DC across red and black, but I'm seeing nothing. Does this suggest a PCB fault?

    Basically I dont want the engineer to come along and start by replacing the aquasensor if that's not the problem.
     
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  3. picasso

    picasso

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    Got any voltage between red and the chassis.
     
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  4. whistler

    whistler

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    Sorry haven't had chance to check this and expecting the engineer this morning

    UPDATE: Engineer didnt turn up! Checked voltages again and there is 4.6v on the red. Turn the tap on and green rises to around 2.5v which I assume indictates impeller is rotating. But the boiler still does not recognise demand for hot water.
     
    Last edited: 15 Jul 2020
  5. picasso

    picasso

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    Check d22 and see that its set to 1.
     
  6. whistler

    whistler

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    No, it stays at 0 when taps turned on.
     
  7. picasso

    picasso

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    Certainly looks like the board but its your call as I am not in front of your boiler.
     
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  9. Gasguru

    Gasguru

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    Turn comfort mode on (rotate DHW temp control fully clockwise and back a bit), does it fire up?
     
  10. whistler

    whistler

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    Yes it does fire up in warm start mode which gives us a small amount of warm water so the gas valve ignition side of things seems to be ok.
     
  11. whistler

    whistler

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    Engineer arrived today. My previous engineer has recently retired and he recommended this guy to continue servicing my system.

    Basically he opened the boiler front panel, asked me to turn on the hot water and observed that the boiler wasnt firing up. Then without any diagnostic testing he proclaimed that a new sensor was required and off he went to order a replacement. I didnt mention that I had already carried out some diagnostic tests, as I dont want to tell him how to do his job.

    I do hope his diagnosis is correct!
     
  12. picasso

    picasso

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    Keep us posted on the outcome.
     
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  13. Gasguru

    Gasguru

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    To be efficient you tend go with the most likely fault...

    99% of the time it will be the impeller breaking up so either replace the whole brass lump or just the innards.
    0.5% it will be a faulty mixer tap pulling in hot via the cold pipework and not through the boiler
    0.5% the pcb.

    But there's always the weird fault that catches you out and you look like an idiot in front of the customer :)
    Most gas engs. wouldn't attempt to measure the Hall output...it's beyond their knowledge and it's certainly no mention in the manual about doing so.
     
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  14. whistler

    whistler

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    Update. The boiler started working again, although intermittently. The engineer changed the impeller and all seems to be ok now. It occurred to me that a few days before the fault occurred there had been a burst water main in the area and water had been turned off for a few hours. Maybe sludge in the water when it was turned on again had bunged up the impeller?
     
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