Hi! My problem is that suddenly my 12-year-old Weil McClain natural gas boiler stopped responding to my thermostat and simply remained on until I manually turned it off using the on/off switch on the boiler itself. (It does go off when the water temperature got hotter than the max setting, though.)

So at this point, I'm just trying to figure out where the problem lies: a)the thermostat itself b)some other electrical component, presumably on the boiler itself or c)something else entirely.

Any input would be enormously appreciated.

the most DIY-ish repair on a gas heater is to carefully replace the thermocouple. failure of that sensor means the furnace or boiler doesn't turn on.

IMPHO this is a controls issue, which brings up a safety issue of high priority, especially since it won't turn off. you need a heating pro, and quickly.

I agree with swschard. You need heat fast so call a pro. Trouble shooting your problem via the net is risky. Could be your thermostat, [thermostat wiring, most unlikely, but still possible] or even your aquastat. It is possible to test all three but that would depend on your homeowners skills. By doing it in a certain order you can find the culprit. {My money is on the aquastat.} But that is a net guess.

This message has been edited. Last edited by: CommonwealthSparky,

Hi guys, thanks for your ideas.

Actually, it turned out to be a short in the thermostat, and with the thermo's successful replacement with a brand new one, my boiler is no longer the spoiled, defiant child but a nice, docile, scholarly type, doing just what I tell it to do!