Burner won't light with thermostat

[Spike40]

My neighbor has a pool I am troubleshooting and all the block diagrams have turned up no bad components yet. I have not tried the voltage tests yet. The burner will turn off with the t-stat but will not turn on when calling for more heat. Any help, I'm doing as a favor (am electrician)!

[PoolCanada]

I have similar problem. If I turn thermostat to higher temp, it turns off in a few minutes. The Pilot light is also turned off at the same time. I have to do manual light up all the time. If I keep the thermostat in the middle, the heater can be on for a very long time until it turns off itself. Sometimes totally "off", sometimes temporary "off". Is there a way to fix the component instead of replacing it?

[PoolDoc]

Hi Spike;

I'm going to offer a suggestion, and then give you some bad news.

Here's the suggestion: you may be looking at a millivolt heater driven by a "thermopile". These are operated by a pilot light that heats the thermopile, generating barely enough electricity to operate the gas valve. Even small amounts of corrosion can render these heaters inoperable. But, what also happens is that the pilot can become weak, or the thermopile can be weak, in which case it will hold hold the valve open, when after a manual start, and may even work properly so long as the extra heat from the complete burner is present. But, when it has to run on pilot alone, there's not enough 'juice' to operate.

Typically, the fix is to replace BOTH the pilot AND the thermopile, so you can simultaneously eliminate problems from both sources.

Of course, this only applies to a millivolt heater. If your heater has a 110V supply . . . then I don't know.

OK, bad news. We don't do 3rd party support. I've started the PoolForum over 15 years ago, and I'm not sure I've even seen a case of "I'm helping my neighbor" go well. If he wants help, he can register. You can even post together. But there's too much running back and forth between the net and your neighbor for this to work out.

So . . . I am NOT upgrading your membership.

[Spike40]

Thanks for the extra input. This does sound like a possibility. The good news for me is that I am benefiting from their pool as they are elderly and happy that someone is using it more frequently. I feel that the least I can do is offer some help (along with dinner invites etc.) They as I stated are elderly and hardly know what a computer is. His pool guy is trying to sell him a $350 plus gas valve and I really don't think that is the problem what so ever. Just trying to keep them from getting into the "let's try this..." syndrome.

Thanks again.

[PoolDoc]

Good luck.

I rapidly learned to hate older millivolt heaters -- you could fix what was broken, but then still have problems. The available current was so low, that any corrosion on any of the connections or terminals tended to cause a problem. And, when you mix chlorine fumes (from the ubiquitous trichlor) with wiring, you ALWAYS get some corrosion.

Working your way through wiring snaked around inside floppy sheet metal, cleaning terminations did not pay well (since it was usually a do-over) and almost always ended up in cuts on my hands.