uncommanded heating

the65dartguy1

I have a Dunkirk boiler model PWX-5VNT2 that has been running when it is not commanded to. For example the thermostat is set to 66 degrees and the the actual temperature is 74! This is a true in both zones of the house. I have replaced the batteries in the T-stat in the main zone of the house. Boiler seems to be functioning normally otherwise. ANy thoughts or ideas? My gut reaction was the something went bad in the circuit board, but its status light says it is OK. It looks like a rather expensive part to just swap out and be wrong!

Abracadabra

do you have a separate domestic hot water heater or does the boiler also heat your domestic hot water?

the65dartguy1

They are separate from each other.

Abracadabra

Disconnect thermostat wires at boiler. If boiler still fires on it's own, then circuit board is suspect. Otherwise could be issue with thermostat wiring or thermostat

the65dartguy1

Thanks for the input. One thought i had... Could the t-stat and or wiring even be the case if there is two zones though? I would think that that would say the circuit board, but this is all guessing. I will try the t-stat wires like you suggested when I return home later. For now both t-stats are switched off, so if the temp is the same upon arrival it would have to be the circuit board, correct?

ChrisJ

Disconnect thermostat wiring at boiler, if it shuts off then disconnect thermostats and reconnect wires to boiler. If it's still off connect one thermostat at a time until the boiler turns on for no reason. Be sure to keep wires isolated from each other before connecting thermostats of course and I'd cut power to the boiler while performing each task.

This is how I'd do it if I didn't have a multimeter.

the65dartguy1

Good idea. I will try that.
I do have a multimeter, just not sure exactly what I should be looking for. I work on all sorts of stuff, but residential heating and cooling is not really anything I've messed with much.

ChrisJ

If you have a meter, you could disconnect the thermostats and take an ohm reading between R and W on the thermostat to see if either are closed (on) when they should be open (off).

But it may actually be faster to do it the other way now that I think about it.

JUGHNE

If you have zone valves with end switches that turn on the boiler and pump, one of them could be stuck. Disconnecting the wires at the boiler would be a start.

the65dartguy1

I do have zone valves. I disconnected the wiring coming out of the valves going to the boiler and it continues to run.
So circuit board maybe? Definately seems to be in the boiler itself.

JUGHNE

I would disconnect the wiring AT the board itself. Actually disconnect all control wiring at the boiler and see it has still has a mind of its own.

Tim McElwain

Do you have a vent damper on this boiler?

Tim McElwain

What is the make and model number of the electronic control?

todd_ecr

Tim, those use a Honeywell L7148 electronic aquastat. Those are obsolete now through us, but we do have a replacement kit available.

I agree with the others. Isolate the boiler control circuit (T-T). This will give you direction in troubleshooting.

the65dartguy1

So it turned out to be a zone valve motor. I did not see the pigtail to the other box and thus the heater kept going. All is well in this little part of the world again.
Thank you all very much for your help, it truly is appreciated! This site really rocks!
I will be back, though hopefully not soon!