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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21761
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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Ive got a weil mclain boiler and the burners aren't working,

Customer Question

ive got a weil mclain boiler and the burners aren't working
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: well the boiler has been shut down since last winter because i was adding some baseboard heat
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: yeah i jumped out the thermostat at the boiler
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: i changed the thermocouple and the pilot is fine however i don't know why the burner won't ignite
Submitted: 9 months ago.
Category: HVAC
Expert:  Rick replied 9 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

What is the model number of your boiler?

Customer: replied 9 months ago.
weil mclain cg
Expert:  Rick replied 9 months ago.

Do you have electronic ignition or a standing (lit all the time) pilot?

Customer: replied 9 months ago.
Expert:  Rick replied 9 months ago.

Is the motorized damper open?

Customer: replied 9 months ago.
the damper is the vent that comes out of the top of the boiler?
Expert:  Rick replied 9 months ago.

The damper is in line in the vent (see attached pic). When it's open the flats on the motor shaft will be vertical.

Customer: replied 9 months ago.
This is what I have
Expert:  Rick replied 9 months ago.

Looks like somebody removed the damper. Try pressing the reset button on the blocked vent switch on the side of the bell shaped draft diverter on top of the boiler. If you push the small button between the 2 wires and it clicks you have reset it and the boiler will fire up with any luck. I'm assuming the pilot is lit.

Customer: replied 9 months ago.
The burners lit up before I even pressed the reset button. I lit the pilot, jumped it out, and turn it on. Also do I need a new damper?
Expert:  Rick replied 9 months ago.

Dampers are a waste of money. You'll never get back in fuel cost saving what it cost for a replacement. It's only there to help hold the heat in the boiler when it isn't firing.

Customer: replied 9 months ago.
Is there another reason the burners weren't igniting before? They have lit before and just went out
Expert:  Rick replied 9 months ago.

Was the pilot lit? If so then the boiler has to be down in order to troubleshoot this. It's an old boiler. The gas valve could be failing or maybe you have a bad connection.

Customer: replied 9 months ago.
The boiler is shut off. I was thinking the gas valve is bad. I don't know how to troubleshoot that though
Customer: replied 9 months ago.
the pilot was lit
Expert:  Rick replied 9 months ago.

You can't unless the boiler isn't working. When it doesn't fire up and it should (call for heat boiler & is well below high limit setting) you need to check for 24 volts AC at the gas valve. If you have 24 vac a lit pilot and no burner igition then you have a bad gas valve.

Customer: replied 9 months ago.
24 volts on these 2 wires?
Expert:  Rick replied 9 months ago.


Customer: replied 9 months ago.
I don't have a voltmeter on me right. Ironic since I'm an electrician. However I can only assume that if I'm not getting 24 bolts the gas valve that it could be a problem with the transformer?
Expert:  Rick replied 9 months ago.

Given that it's starts back up own its own then yes a bad transformer is likely. R & G terminals are thermostat, R & C are 24 v constant. Besides the vent switch the only other things in the circuit are the aquastat/limit and the rollout flame sensor down by the burners. Rollout is 1 time use. If it's open it has to be replaced. Here's the schematic (with damper in place)

Expert:  Rick replied 9 months ago.

I'm logging off for the night. I'd appreciate a favorable rating. This thread won't go away and I'll answer related follow ups even after you rate me favorably