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Boiler won't fire back up

1013 Views 4 Replies 3 Participants Last post by  danpik
I have a Weil-Mclain boiler and I recently replaced two radiators. After I turned the system back on it fired up fine, but then I noticed I had a bad solder joint near the new rads. I powered down the system and drained it to fix the leaky joint. When I turned the system back on the pilot lit, the circulator ran, water was moving through the pipes, but the boiler just would not fire.
I tied the thermostat wires together thinking the thermostat might be the issue, but no change. I also swapped out the transformer on the system, but again nothing.
Any ideas?
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...the pilot lit ... but the boiler (main burner) just would not fire.
Any ideas?
Start with the thermocouple to be sure it's producing enough power.
It's probably fine but is inexpensive and often the culprit.
Similarly... touch and tighten all the wiring connections.

The next step up is the combination valve itself.
The same control voltage running the thermostat and pump relay should be feeding the valve too... either there's a fault in that circuit telling the valve to open or the valve itself is bad.
Is this an electronic ignition or a standing pilot system?
It is a standing pilot system
If it is a standing pilot then it should have a thermocouple like this...

If the pilot is staying lit then it is good. Check the wiring going to the gas valve to see if you are getting 24 volts there with the thermostat calling for heat. Check between the TH and the TR terminals with a meter.
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