My boiler wouldn't light this morning and after troubleshooting it, I found no control power past the POC switch in one of the gas valves.  I have never had an issue with a POC valve much less never had to work on one, so I would like a little education on them.  To that end, pretty safe bet a POC valve is a safety to prevent raw gas from blowing through the boiler during pre-purge?  With my issue being the POC valve, what is the best way to test it to determine if it is a stuck switch or if the valve is indeed not closing?  My POC valve is a Seimens.  This happened once before about 4 months ago but as I and PBBS were troubleshooting it, she suddenly kicked in and began working, and we were not able to get it to fault out again, so we never did figure out what the cause of the shutdown was.  Any advice?  Thank you.

Cheers

Jeff Gardner - Plant Engineer - Heathcare Waste Solutions, Inc.

Can you tell if the valve is shut all the way?

Siemens documentation states that POC valves are not adjustable and suggests replacing.

If the valve is not functioning properly the only entity that can repair or rebuild the valve is the original manufacturer.  If you attempt to repair or fix the valve, the valve is no longer UL listed, and this is a violation of state statute.

If this valve is not functioning properly it could cause a furnace explosion.

Replace the valve.

Joel T. Amato                                   

Chief Boiler Inspector

Proof of closure switches in Maxon gas valves can be checked by seeing if the relief vent between the two gas vales is building pressure.

We do this on an annual basis because the first valve in line could leaking and you'll never know it, even if the proof of closure switch is made.