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Boiler doesn't fire up intermittently

I have the following condition:

When the thermostat or hot water tank calls for heat, the circulator pump would turn on, but the boiler would not fire up. The pilot light is lit. I would have to turn the system off via shut-off switch, and when I turn it on, everything will work as it should.

This first happened in May of 2021. It has since happened once a month since October. I'm not sure where to start with troubleshooting. Any and all suggestions would be greatly appreciated and welcomed.

It is a three zone hydronic heating system running on a Weil-McLain gold CGa gas-fired water boiler. It is controlled by a Taco 3 Zone Switching Relay w/ Priority SR503-EXP-4. The switching replay was replaced in August.

Comments

  • HVACNUT
    HVACNUT Member Posts: 6,331
    On the SR503 check the connection from XX to the thermostat connection at the boiler. 
    If that doesn't work, turn off the power and check all connections at the boiler, including (especially) grounds.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,477
    Sound like the boiler is going off on "lockout" Shutting the power on and off resets this.

    Could be flame igniter, flame sensor or flame signal pressure switch etc.