Boiler will not shut off

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Stevo

Check to see if you've got water in the boiler. This way you'll make certain that the aquastat is sensing the water temperature.

What does the wall thermostat operate? Does it operate a zone valve, that then opens and a end switch makes contact to turn on the gas valve after going thru a aquastat and a high limit?

Is this a millivolt system? Less than one volt to run the boiler? Check wiring for a short.

If gas valve is 24 volt, turn off main power supply from breaker box to the boiler. If gas valve shuts off, okay, if not gas valve sticks open and gas valve defective.

We have not got much left. Turn off power, remove one wire from the aquastat control. Make sure wire isn't touching any metal, turn power back on. The gas valve shouldn't come on. If gas valve opens, you've got a short in the wiring.

Take the front cover off the boiler by the gas valve, try to have the boiler running, is the flame rolling out, and hitting the gas valve and touching the wiring? Insulation in the wiring shortened out from the flame. Gas valve sticking in the open position from excessive heat. If this is the case the heating surface of the cast sections will have to be cleaned before replacing any parts.

If you feel uncomfortable working with this, please do not attempt, and call a heating contractor.

John Hutfloetz