Glow worm compact 100e - woes

Discussion in 'Plumbing and Central Heating' started by beefster, 2 Nov 2010.

  1. beefster

    beefster

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    It started as something so simple. Boiler ran ok but loosing pressure through the PRV - which i replaced. Here starts the tail of woe...

    First - no fan on ignition! Found loose connection in supply. Reterminated ok. Then tested.... then had some arcing on the PCB.... which i dont believe was wet at all.... from a transistor (i think).
    Now the main gas valve does not seem to be opening fully. Have ignition and a very small flame encirles the ignition probe, not enough for the sensor to be happy and lock out.
    Now i am pretty certain the card has gone - arching etc. No visible damage though.

    Q. No U gauge with me so.... want to check the PCB output... how do i test the power supply to the gas valve???
    Valve is a Honeywell VK4104G. What voltage should i expect on the feed to it on ignition?

    Am i missing something?

    ta
    Kev
     
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  3. beefster

    beefster

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    Rang Glow worm tech desk - very helpfull but....
    Said i should have between 24v-50v ac on the white and black.... i have 233 DC!!

    Will this have buggered the coil too now........ All started with a minor drip! now looking at £150 for the pcb and possible a new gas valve too!

    Deep Joy
     
  4. Rob

    Rob

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    Why are you measuring dc when your looking for ac
     
  5. Gasguru

    Gasguru

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    The vessel schrader is difficult to access on these...normally need to bolster a lump out the wall to get the pump on...hence PRVs often leaking since no-one will have sorted the vessel.

    As for the gas valve forget what Glowworm tell you...they haven't a clue. The gas valve is driven with a pulsed waveform and the voltage you read will vary dependent on how the multimeter interprets it.

    Low burner pressure is a common failure mode for these pcbs. Replacement is NOT a diy job since requires setting up.
     
  6. beefster

    beefster

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    Ac / Dc - my fluke meter measures both on the same setting. Flashes up whether its ac or dc voltage.

    Replaced PCB and all working fine again.

    Will check the water pressure out regularly over next few days and keep an eye on it.
     
  7. Agile

    Agile

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    I am glad that its working again. However, the expectation is that a failed PCB after changing a PRV implies you spilt water on it.

    Its not much use to have a meter which you cannot specifically select to read AC or DC for boiler repairs.

    In any case I doubt that it can actually read AC superimposed on DC and give both readings.

    Tony
     
  8. beefster

    beefster

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    More woes.... :(
     
  9. beefster

    beefster

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    Ta Tony, you maybe right but did wrp PRV in a rag while removing and didnt see water in the tray etc??
    The meter is the a fluke multi meter i use at work as an electrical engineer - I have faith in them. Industry standard and bloody expensive. A transistor looks to have burnt out on the card in the gas valve power supply cct so going to "try" and get that replaced and test the card. If i can find what size and type it is... prob a trade secret. :?:

    Boiler is now tripping on overheat when the DHW supply is called. Does not appear to be modulating the burner at all. Hot water goes hot/ cold/hot/cold as burner cuts in and out rather than moduates. Then trips, i am assuming on over heat.
    The last time this happened it was the DHW plate heat exch that was partially blocked.

    Deep joy! The pressure is going up and down in CH mode - Expansion Vessel has water at the test point! So thats in need of replacement. Boiler has to come off the wall to do it on this model!!

    Its rated a "D" for energy consumption....... Is it time to change??
    10 years old??
     
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  11. Gasguru

    Gasguru

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    PCBs on these are carp. Fitted one on Saturday which replaced one only 3 years old. Normally they fail by not ramping up from ignition pressure to max...this one sat at the minimum pressure.

    I assume you mean the pressure has hit 3 bar and opened the safety valve. As I said the vessels are often flat. If you can get to the scrader on the LHS, jam the vessel away from the wall, knock a lump out the wall...you will be able to re-charge it. Boiler off the wall for a PRV...not in my experience.


    Are you a rgi? since the burner pressures require setting from the board pots. I have found new pcbs can be wildly out since pre-adjustment is carried out on the gas valve.

    The thermistor and temperature control on these models is hopeless...dumb Honeywell design. The slightess debris in the primary side of the plate will result in a lack of modulation. Turning the DHW temperature control down a little can sometimes mask the problem. Of course if the correct burner pressures are not set this could also be a reason.
     
  12. beefster

    beefster

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    Sorry Guru, meant the expansion vessel had water at test point - hence boiler off wall to replace it. This prob caused the PRV to blow and not re-seat.

    I have had to replace the DHW plate Heat Exchanger twice which with a top feed kit also means boiler off the wall - well not fully off wall but but have to disconnect the top fill kit pipework thru the back of the boiler and its a right fiddle to get out.

    New PCB fitted a few days ago and the DHW is not modulating at all. Trips after two or three cycles on overheat. Wife says she noticed shower going hot/col/hot whilst i was away prior to it failing fully.
    As its a new PCB board i am thinking either DHW thermister - (as it was a new PCB kit should the thermister have been included?? The wire to it was??). Or possibly the Gas modulation coil has gone!

    I have had nothing but grief with this thing! As said i am seriously thinking of cutting my losses and getting a new one fitted.
    It is approx 10 years old and as it is "D" rated......????

    Ta for the advice.
     
  13. Gasguru

    Gasguru

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    Forget the D rating...my boiler is 55% efficient and open flue but has had no parts in 15 years...likewise you'll find many gas instalers are running museum pieces :) My gas bill went down last year despite the extended cold spell...wear another jumper ;)

    Can you install another expansion vessel elsewhere and leave the existing in place.

    I fitted a new pcb on saturday....had the Honeywell clip on flow thermistor. New harness included. Perhaps the new thermistor has different characteristics to the exisiting wet pocket type. As I said the pcb needs setting up. Have you tried turning down the DHW tempertaure a tad. Often this can be sufficient to allow proper modulation (and proves slighty blocked plate)

    I look after about 10 of these. They have their problems but so do new boilers :rolleyes:
     
  14. mickyg

    mickyg

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    get an RGI in, you need to set the boiler up by measuring the gas pressure. This is not a diy job.
     
  15. beefster

    beefster

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    Ta Guru - Thought about the vessel elsewhere. Could fit it in the loft above the boiler easily.

    Fitted the new main flow thermister as instructions. Didnt come with a DHW thermistor though?
     
  16. kevplumb

    kevplumb

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    make sure it can't freeze if you do ;)
     
  17. Agile

    Agile

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    You seem to have a good few boilers!
     
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