Take a look at the t- stat if its stuck that will cause the symptom you describe as well as a bad gas block/valve.

Ive had two fail in two years.

Do you have a salt water pool by any chance?

Davegvg

Yes i have a salt water pool. Is this part of the problem?

How do I check for a stuck t-stat? Is this a diy repair?

Thanks for the info!

thanks Dapooltec - I wrote up but for some reason I must not have submitted a virtually identical answer.

If you dont have a one way trap between the heater and teh chlorinator you will corrode the "thermal regulator quickly"

Davegvg

need to have service person check flame sensor

In a master temp?

natural gas or propane? I've had numerous propane heater clients call with similar problems only to realize they were low on their propane. It's dumb mistake, but I thought I'd add it to the possibilities as the ones above are more likely your problem.

Heaters are not something a novice should be troubleshooting, given the complexities involved.

Having a salt water chlorine generator does not impact the thermal regulator. Having incorrectly kept chemistry can. So too, can a low flow condition, whatever the cause of that.

Without knowing the whole picture of how you particular system is configured, i.e. pump, filter, chems, etc..., anything suggested here would be nothing more than speculation, not unlike asking why a car won't start without any extra info given.

Please get it checked by a professional. There are too many things that can contribute to these symptoms.

Scott

Poolguynj is incorrect in regards to the thermal regulator not being impacted due to salt water. I am a licensed pool professional in Texas with 33 years experience and I have seen it first hand were a thermal regulator disintegrates with salt water pools. The NJ in your name most likely indicates that you are located in the north were salt water generators run at a lower percentage rate and you don't see the damage to the equipment were here in Texas we have to run our generators at a much higher percentage rate year round to maintain proper chemistry causing the parts in the system to fail faster.