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Older gas boiler pilot light going out after running OK for hours

mixelangelo Member Posts: 3
Hi there. I bought a 104 year old house last year in Vancouver, BC with hot water heating, mostly with old cast iron radiators but with some baseboards as well in the basement. The boiler is a 34-yo Super Hot, 100k BTUs. The house is 3000sqft spread across 3 floors, each with its own zone.

Please forgive any vagueness or inaccuracy in terminology in what follows, as I am a layperson and still learning a lot about boilers!

I had the boiler inspected at the beginning of last season (fall 2021) and it ran well all winter long. (Not particularly efficiently, but it worked.) The pilot light went out twice, both times on very windy days, but I was able to re-light it without a problem. In May I turned the boiler off entirely (possibly a mistake?). After starting it up again last week, it ran for a few hours and brought every zone up to temperature, but after a while — and I *think* it was a while with no zones calling for heat, but I could be wrong — the pilot light seems to have gone out. The knob on the gas valve was still set to ON, of course, but there was no "hiss" of flowing gas (and I could not smell any either).

I got an "inspection" + service from a local company. (The fellow who inspected it last fall is no longer available, so it's a different person/company.) He initially said the issue was likely to be a defective heat exchanger that was causing the system to get too highly pressurized, triggering a safety mechanism that cuts the gas. But I am not sure that he did a proper inspection; this was his hypothesis based solely on my description of the problem, but he didn't witness the problem occurring, nor, I think, did he look at the heat exchanger. He generally seemed to think that the system was beyond its useful life, though I've not had any other problems with it (e.g. no leaks, that I have seen, at least).

He did replace the thermocouple and tighten a connection on the pilot gas line, which he then said might be the actual problem rather than the heat exchange. But that did not fix the problem; the pilot light went out again a few hours after he left.

I spent some time watching the boiler yesterday evening and I noticed a few things, not sure if any/all of them are relevant:
  • The light put off by the pilot light is usually blue, but sometimes the flame sounds a little bit "raspy" / sputtery and it is occasionally quite yellowish. (Given the angle the boiler is installed at it's hard for me to see the pilot light directly, but I can see the light it's putting off inside the boiler.) I did mention this to the service tech and he seemed to think that tightening the connection on the pilot gas line would fix the problem, but unfortunately it did not.
  • The pressure gauge on the boiler itself does not seem to work (the needle never moves), though the temperature gauge does seem to work. The newer-looking pressure gauge on some piping nearby sits at 19 PSI after the system has been running for hours. See pics below.
  • I noticed that even though the High Limit temperature on the boiler is set to approx. 190F, the temperature on the boiler temperature gauge never really exceeds 150 or so.
  • It does seem to be short-cycling: the burners will fire for a few minutes, then turn off (before the thermometer indicates the water temperature is anywhere near the High Limit set on the device), then fire again for a few minutes, etc. I'm not sure if that's normal.
My main questions:

1. Most important: To what extent is the system safe? As I mentioned, when the pilot goes out, the knob on the gas valve is still set to ON, but there is no evidence of gas flowing, so it seems that so far the gas is properly shut off by whatever safety mechanism may be triggering (?). But I'm really not interested in having the house blow up.
2. Any ideas on what the problem could be?
3. Overall, is it just time for a new boiler, or with a fix might this 34-yo workhorse still stand a chance for a year or two?


I get the feeling the installation is a bit of a mess; the house inspector passed it when we bought the place, and yes, I know they don't often know what they're doing (and neither did I, especially at the time); but this is the way things are.

Overview (pic taken when system was cold this morning)

Thermostat / pressure indicator on boiler after it has been running for hours

"Other" pressure indicator after it has been running for hours

Thank you so much for any insights you might be able to offer!


  • mattmia2
    mattmia2 Member Posts: 7,148
    Find a competent tech. None of that is how you troubleshoot a pilot going out. My bet is on the regulator at the meter but it could be the pilot burner is dirty or the regulator for the pilot is bad in the gas valve too.

    They should have checked the gas pressure on both sides of the valve and checked the voltage from the thermocouple.

    On a hot water boiler a failed heat excanger will have water leaking out of it.
  • pedmec
    pedmec Member Posts: 712
    I hope that's a propane system. (I see copper going into the gas valve)

    The problem with changing the thermocouple is exactly that, changing the thermocouple. Tech should have cleaned or replaced the pilot assembly. I find half the time that techs change the thermocouple they don't even realize the flame is barely striking the thermocouple. it works for a little while because its clean but eventually it gets dirty and can't generate enough enough millivolts to keep the pilot valve open. If the pilot lights but won't stay lit clean or replace the pilot assembly. i say replace because the orifice doesn't always want to come out to clean.
  • mixelangelo
    mixelangelo Member Posts: 3
    pedmec said:

    I hope that's a propane system. (I see copper going into the gas valve)

    It is natural gas. Is this a problem? :# (I am in Canada if that makes a difference re: code.)
  • pedmec
    pedmec Member Posts: 712
    Not allowed here for natural gas. Its a problem if you use methyl mercaptan as a leak finding agent in your natural gas. the copper reacts with the sulfur in the methyl mercaptan and corrodes the copper.
    JUGHNE Member Posts: 10,278
    40+ years ago our NG company would not allow any copper for gas piping.
    The reason given was the sulphur in the NG itself would corrode copper/brass.

    The only copper allowed then, was outside for yard lights. And that copper was internally tinned for protection.
    Both the tinned copper and yard lights have long since been gone.

    Since then copper is allowed in the system as the gas is reportelly cleaner than it was.

    Mix....the best thing you could do is check with your NG provider concerning its use.
  • mixelangelo
    mixelangelo Member Posts: 3
    Thank you all for the very helpful feedback on what to look for in a service tech visit, and on the copper line. Will update this if/when I finally resolve the issue!