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Pilot light goes out when gas valve opens

I have a gas-fired steam boiler which now won't light when you call for heat. The pilot light is on, but then as soon as the main gas valve opens the pilot light goes out. Actually, the pilot light doesn't totally go out, because it comes back once the gas valve closes. But presumably it gets too small to actually light the boiler (maybe it would light if I let it sit there with the gas on for a long time, which I don't want to do).

My best guess is that the pilot light tube is clogged and there's a pressure drop when the main valve opens that is enough to almost put the pilot light out. Would cleaning or replacing the pilot tube fix that? Or might it be the combination gas valve? Any ideas for how I could narrow the problem down more? Boiler is 20+ years old, and I've never had any problem with the pilot light before (save for a bad thermocouple once). Any tips appreciated.

Comments

  • Steamhead
    Steamhead Member Posts: 15,752
    Time to call a pro. This can be a dangerous situation.

    If there is enough gas pressure to feed the pilot until the main burner kicks on, your gas supply is restricted in some manner. Have a pro check the incoming gas pressure with the main burner off and then on. If the problem exists on all gas appliances, there is an issue with the service piping and/or meter, for which you'd need to call the gas supplier.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    mattmia2
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,096
    Yes, call a pro. @Steamhead advise is on the money
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 7,143
    Is it natural gas or propane? Is there enough gas in the tank if it is propane?
  • Sethamin
    Sethamin Member Posts: 58
    Turns out it was the combination gas valve that was the problem. Likely some debris got stuck in there and was causing an obstruction. Replaced it and everything is good now.
  • pecmsg
    pecmsg Member Posts: 3,532
    Sethamin said:
    Turns out it was the combination gas valve that was the problem. Likely some debris got stuck in there and was causing an obstruction. Replaced it and everything is good now.
    How does enough Debris get in there to block it. 

    Where’s the sediment trap?
    lines properly sized. 

    Something is Wrong!
  • mattmia2
    mattmia2 Member Posts: 7,143
    did a professional with combustion analysis equipment that knows how to use it replace and adjust the new valve?
  • Sethamin
    Sethamin Member Posts: 58
    Yes, I had my HVAC company properly replace it.
  • pecmsg
    pecmsg Member Posts: 3,532
    Sethamin said:
    Yes, I had my HVAC company properly replace it.
    With a combustion analyzer?

    where’s the print out?
    SuperTech