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AO Smith boiler (not) firing...

3 replies [Last post]
Joined: Aug 6 2009


We're newb Eichler owners, still in the honeymoon period - until today. Moved into our atrium model in February, and used the apparently-well-maintained radiant system plenty during the cold spells up into the springtime. Now that we're getting cold again, we turned up the thermostat this morning but with disappointing results.

The pilot is lit, the spark plug(?) fires, and the burner lights up - but then, the system snuffs out about 5-10 seconds later. About 25 more seconds, and the cycle repeats (preceded by some rapid ticking)...

Any idea which piece of the puzzle might have failed? Or if there is anything I can do to troubleshoot?

Thanks a bunch
=- Joe

Joined: Mar 21 2003

We got rid of our AO Smith boiler a couple of years ago so I don't remember exactly how it worked. But typically there is protection against the burner not coming on and against overheating.

So, in order, I'd do the following:
1) Call a qualified boiler maintenance person.

If you insist on doing it your self,
2) See if the pump is coming on. If the water is not circulating then the boiler might overheat and shut down.
3) See if all the little metal rod things (thermocouples) on/near the burner look like they are in the correct place and not dirty. One of those checks if the pilot is on and turns things off otherwise. That one is working in your case but there might be another one for checking if the burner came on.
4) Do a Google search on AO Smith and/or generic natural gas boiler valve/control assemblies and see if you can read up on how they actually work.
5) Go back to step 1...

Joined: Apr 20 2006

Tod's advice is 'spot on'....especially good is the first part about calling your 'soon to be' favorite radiant heat contractor.
It sounds to me like the recirculating pump is not working. They usually start circulating as soon as the thermostat turns the system on. There are overheat sensors on the unit that will shut off the gas when overheated. I think you will be pleased at how inexpensive a service call can be.
Randy from Dura-Foam Solar Center

Joined: Dec 20 2004

Yes something similar happened to me. They never tell you that you should turn on the heater once a month to get the pump to circulate as it is lubricated with water(? - That’s what I was told but never googled that fact) and can seize up. And the Service call is cheap, the new pump installed was 400 bucks.

When the thermocouple went out (in this case it will not stay lit) PG&E will come out and diagnose this for free. If you’re in a hurry, just let them know you think you smell gas (I really did) and they will send someone out on the same day. PG&E even has a spare thermocouple if yours is the right length (mine was too long.)

Anyways I got rid of the boiler on its 50th birthday and got a Takagi tankless heater and it heats faster and my PG&E is lower.

-- Ralph

PS Marty, you should write a New Eichler Owners handbook :-)

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