Gas boiler shuts down in a couple of minutes

[jpaul]

Old boiler with baseboard maybe 1960's, I don't know. Only one zone.

Boiler idle since last heating season. There was a chimney problem...the flue fell. New stainless external chimney now in place.

Went to light but no pilot light, unclogged jet and have beautiful pilot light.
Turn on, call for heat and fires right up then shuts down in a minute or two and I see the temp is 200 degrees. Let cool down fires up, reaches 200 degrees and shuts down.

When calling for heat I heard lots of gurgling so I looked into bleeding system. I have three valves one at the water inlet, one under small expansion tank and the drain valve:

A couple of questions:

How do I bleed this system and is boiler on or off during bleeding. If on, and the boiler doesn't stay on can it sill be bled?

This couldn't be be a thermopile problem, correct?

When the stainless chimney guy was working on the chimney he broke the air vent and it was leaking and he replaced it. Leaked a good amount of water. I asked if the boiler would need to be bled he said it would self bleed.

If it's a matter of bleeding I'd like to beed it and test it…Anything other then a thermopile replacement I'll call someone in but I'd like to have an idea of what the problem might be before I call. Thanks for reading, any comments appreciated.

 

[Dana]

This is 99% likely to be an air-purging problem. With air in the system you are getting no flow, and without flowing water taking the heat away the boiler hits it's high limit and cuts out. When the guy broke the vent and replaced it, air got into the system, and he didn't succeed in fully purging the air sufficiently for the pumps to keep the water moving, with an air-bubble in one or more of the pipe loops, a condition alternately called "air locked " or "vapor locked"

The best place to bleed air out of the system is at the highest elevation on the system, not in the basement. There will usually be bleeder valves on at least one, but sometimes every baseboard & radiator on the system, and often an air trap/vent on a stub of pipe too.

Baseboard bleeders come in a few form factors:

Poke around upstairs, see if you can find one or more. If the boiler is at 200F be sure to use gloves when bleeding it. Turn the valve until you hear the hiss of escaping air and keep going until it's mostly or all water, not air coming out. If you have multiple bleeders, do them all.

Eventually you'll relieve the air locked section enough for the pump to keep it going, and the bubble-trap/air vent on the boiler would eventually take care of it.

 

[Sponsor]

 

[jpaul]

Looks like I have a small cap at three locations so I guess the cap covers a bleeder. I check it out, thanks.

 

[jpaul]

This did it thank you very much. Water bled out for 30 seconds or so then air for 30 seconds or so then water . It fired up and stayed on. Thanks again!