Hi! Actually, I think I know enough to know I don't know enough to fix this myself, so I'm just trying to make sure I know what's likely malfunctioning so that I'm not taken advantage of by the repair people.

Here's the problem. I have a 12-year-old (approximately) Weil McClain natural gas boiler, (not connected to my separate water heater), model EG 55 SPDN, that suddenly, today, remained on well beyond the thermostat setting. (It does go off when the water temperature goes above a certain setting, though.) Clearly, it's not responding to the thermostat--I turned the thermostat setting way down and the boiler continues to operate. I have had to turn the boiler off manually, using the on/off switch on the boiler.

So is the problem likely a)the thermostat itself, b)some other part of the electrical system (located, I assume, on the boiler itself), or c)something else?

 

Welcome to the forum.
What type of t-stat are you using?
Have you changed the batteries (if required) in the t-stat recently (long shot, but it could be batteries in the t-stat).

More then likely, it's the aquastat that controls your boiler. Sounds like a relay that has gone bad.
On your boiler, there should be a box that most or all the electrical wires go into (including your t-stat). Can you get the make and model of this unit?

 

Do you have more than one thermostat (zones)?

 

Guys, thanks for your contributions.

Actually, the short turned out to be in the thermostat, and its replacement got an out-of-control boiler nicely reined in! So I won't have to spend another night like last night-- getting out of bed multiple times to manually turn the boiler on and off so we didn't freeze or roast to death!

 

Hi, I ve just had mine fixed. If it helps, it was the wireless thermostat signal needed lowering as it was picking up a neighbours that had just been fitted. It cst me nothing. Worth a check .