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Boiler stops running after a few hours
It is a gas steam boiler with a wired-in thermostat.
Everyday, it always runs first time I turn it on. But it stops running after about 2 hours.
When it runs, I use a multimeter to check and find voltage at the thermostat and between terminals C and R and between terminals C and Y at the transformer.
When it stops running, there is no voltage at the thermostat and also nothing between terminals C and Y. However, there is still voltage between terminals C and R at the transformer.
The vent damper is on always on the "open" mode.
Does anyone know what is going on?