Hi,

In the past month, there have been three times that our gas fired Weil MClain boiler stopped firing, including last night. The circulator pump keeps pumping, the zone valves stay open, and the flue valve stays open. Each time I've turned the master electrical switch off (110V) and then waited about 30 seconds and flipped it on. When I do, the flue valve cycles closed, then opens, then the burner kicks on and we're back in business.

How do I diagnose this?

Is it a spill sensor, thermocouple, or what?

Thanks guys.

yes

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Do you have all the documentation that came with the boiler? The troubleshooting procedure should be contained in them. Some are made easy by flashing lights in a certain pattern.

it is not the thermocouple.
you need an electrical multi tester and you need to check for 24V from the transformer. from there start chasing the 24V to see if it is passing thru the damper and on to the next safety. (which I think is the spill switch. from there it goes elsewhere until it eventually powers the burner.
you will have to wait until it fails to find out where it is failing.

I have to dig out the manual, but the system is about 20 years old and there are no LED's.

So I use the multimeter and trace back the 24V. So I assume somewhere there won't be any voltage. Does that mean the previous part is bad, or the one I'm testing, or what?

You put one lead to ground, and test on either side of a switch. If there's voltage on one side and not the other, it is open.

yeah, but you have to wait for it to fail before you can find the culprit.

by chance is this have a Honeywell smart valve