I recently had to turn off the main valve at my gas meter to cap an old buried gas line to my pool heater that rusted out and started leaking. When I turned the gas back on, the pilot lights for both my water heater and fireplace will not stay lit. I can get both to light up when I push down the pilot button, but as soon as I release it they both go out. Both were working properly prior to turning off the main gas valve. I did go ahead replace the thermocouple on the water heater but it is doing the same thing and I find it hard to believe that it is a coincidence that both appliances are doing the same thing. My gas furnace is firing up normally. What else could be the cause of this?
I had the similar problem couple of days ago.
Was what I would call as strange occurence, after starting heater, heater would shut off within a few minutes but relight and continue the shutting down issue afterwards.
Following advice from many forums indicating a faulty thermocoupling, I replaced the thermocoupling with a new one and results stayed exactly the same.
Turns out the bracket holding the thermocoupling in place at the correct distance from pilot had moved a bit apparently from a couple of years of thermal expansion and contraction- in short when the first shutdown occured there was a loud "pop" as if something had broken and -yes- the bracket moved just a small amount when this occurred, causing just enough diatance to allow the thermocoupling to heat sufficiently enabling start up but after a few minutes of cooler air drafting through the vent- to feed the flame- the thermocoupler was cooling off enough to break contact.
Heater works well now even with the older thermocoupling reinstalled (had to check it's condition out of couriosity) with no issues after readjusting but this was difficult to figure out since the bracket is not adjustable. The key indicator (for me)was the fact the lighter was close enough to become red hot after the flame out and restart each time. After readjusting the bracket (accomplished by causing enough tension with the copper tubes attached to thermocoupler to allow the bracket to remain in proper positioning), the lighter end is not discolored at all after start up and thermocoupler is in the correct close distance from pilot light to enable stable operation of the unit..
Hope this helps.