WM Boiler not responding

Bowhunter74

WM Gold CGS boiler not responding to call for heat, but will turn on when I jump the aquastat on the indirect tank. Zone valve responds to thermostat's call for heat (motor turns and engages activator switch) but it does not turn the boiler on.

What I've done:

1. Checked that 24v are making it through everywhere. The only place I am not getting 24 is from the zone valve to the inside of the boiler.
2. Reconnected all wires to be sure of good connections.
3. Swapped out: thermostat, aquastat, synchro motor in zone valve.

Wondering: Could it be the activator switch in the zone valve? Should I try replacing the whole head? Would that make sense since the call for heat is activating motor, but when the internal switch is depressed, no response from boiler?

Jamie Hall

At some risk of asking the obvious… what happens if you jump the control switch terminals on the zone valve? The ones connected to the boiler? If the boiler then fires… seems like the switch on the zone valve, or the motor, or not actually opening all the way…

HomerJSmith

Yes sometimes the micro switch does go bad. If you jump the end switch terminals (the top two screws on the terminal board) the boiler should fire. If so, the switch is bad. You can replace the whole head or just the micro switch.

Bowhunter74

There are no obvious assumptions with me…I'm learning as I go.

Can you tell me what two wires to try jumping? I've got three pairs of white/red coming in/out in addition to the pair going to the other zone valve (hot water). I also realize the top white isn't connected here—i took the pic when trying something else.

Bowhunter74

https://forum.heatinghelp.com/discussion/comment/1821402#Comment_1821402

Any idea where I might find a replacement microswitch for this model?

109A_5

Hello Bowhunter74,

The terminals are labeled 'End Switch' behind the wires, they connect to the micro-switch inside the zone valve assembly. In either case the switch inside the thermostat device closes (turns on) energizes the zone valve's motor, the motor turns to open the valve, when the valve is fully open the 'End Switch' closes (turns on), then the aquastat is enabled if the water is not too hot the boiler should start up. An open or defective (failed open) switch should have 24 VAC across it, a closed switch should have 0 Volts across it.