Weil McLain PEG Boiler Not Firing

puck8605 · May 23

Hi - I have a Weil McLain PEG series boiler. It's been great and I have maintained it carefully.

However, about a month ago it stopped firing. I figured I'd have the summer to sort it out but we have unusually cool weather up in the Cleveland area at the moment.

Here's what l've done so far:

Replaced t-stat batteries and bypassed the wiring to force it to start.
Checked all connections. The unit is receiving power as the light on the low water cut off briefly blinks and the manual feed button on the water feeder works fine.
The vent damper was not opening. I was a bit hasty and tried to force it open and broke it.
I replaced this with a new motor. It has not moved from the open position (where the motor was in the package) since l replaced it (photo attached).
Bypassed the pressuretrol and vaporstat.
Checked the auto spark and thermocouple. Did not see any noticeable damage.

Based on the fact that the unit isn't even opening the damper, my thought it there's an issue with low water cut off or the ignition controller that's preventing the start sequence from kicking off.

Curious what you all think could be the issue and if there are any additional testing steps that I should take to diagnose (I have a multimeter and probes). Appreciate the help as always.

Thank you!

Grallert · May 23

Is the damper motor getting power? There's an end switch in it or on it somewhere. There is also a bypass switch I think.

puck8605 · May 23

I'm not 100% sure. After I broke the previous motor, it was attempting to move but couldn't because well…I broke it. The new one has been in the same almost fully open position since I installed it.

Jamie Hall · May 23

That damper has to open all the way for the end switch which @Grallert mentioned to close and allow the system to run. If the damper doesn't move at all, there's something amiss either with the new damper or, more likely, the wiring connections to it.

puck8605 · May 23

Ok great. Do I flip the switch to manual on the damper and turn it? Nervous about snapping it again…

Jamie Hall · May 23

Try flipping the switch, assuming there is one, to manual open. Do NOT push on the damper itself… if it doesn't move, it may not be getting power — a wiring problem.

puck8605 · May 23

I was able to successfully open the damper. Once it was open, I flipped the switch back to auto and it closed. Boiler still isn't firing…

Jamie Hall · May 23

OK. Now we need to track down a probable wiring problem. What should happen is that when there is a call for heat — either a thermostat or a zone valve, different systems are wired differently — the first thing that should happen is the damper should open. Then the burner should fire up.

mattmia2 · May 23

there is probably a schematic on the inside of the door for the boiler or somewhere else inside. It doesn't look like it was altered from the factory wiring so that should tell you what operates what from how it is wired so you can figure out which part of the sequence is failing.

puck8605 · May 23

Ok thanks. It was not altered and had been working totally fine. I will do some additional investigation.

mattmia2 · May 23

there are different ways it could have been packaged and installed. if some of the controls were field installed then that won't be on the schematic. if you show us the schematic we can figure out what sequence it is supposed to operate in and where to check.

you can check to see if a safety is closed with an ac voltmeter. if it is 0 vac across it, then it is closed, if it is 24 vac it is open and not completing the circuit. That is for like the end switch contacts on the damper and the lwco. you can see if there is power to the ignition control and work from there.

JUGHNE · May 23

There is usually a "blocked vent switch" under the vent damper, it would have 2 wires going to it. That is usually a very small manual reset red button that pops out to open the safety circuit if for some reason the exhaust gases are not going up the chimney.

There is another safety called the "flame rollout switch", it looks to be connected by yellow wires to the lower left of the gas valve. These are usually one time thermal fused and non resettable. Ohm meter should show closed with wires removed or voltmeter show 0 volts if closed with power applied. Show 24 volts if open with power applied.

109A_5 · May 24

Assuming this is the correct diagram for your boiler. The items annotated in Red (except the ignition module) have to be closed (electrically On) for the Damper to open automatically and then supply power to the Ignition Module.

If I had to guess from here, either the Spill Switch, Rollout TFE, Limit Control (Pressuretrol), LWCO, or possibly the thermostat wiring defect is the issue. Seems you have eliminated the Damper by replacement and the Thermostat by bypassing the wires. A Tech with control electrical experience should find the issue using a Multimeter in a few minutes. If a safety device failed there may be other issues.

BobC · May 24

I'd try unplugging every connector and then plugging it back in. Those connectors are the cheapest thing available and one of the pins might not be making content. Then verify all the safties are closed, the dact your damper iosn't closing on it's own tells me something is open.

Bob

puck8605 · May 24

Thank you so much for the great info here. Planning to do some troubleshooting today. Will report back.

puck8605 · May 24

Well just ran downstairs and resetting the spill switch did the trick. Would never have noticed that tiny button. Thank you all again!

EBEBRATT-Ed · May 24

Just make sure the boiler is drafting or it will trip again and you don't want to have any carbon monoxide issues.

Weil McLain PEG Boiler Not Firing

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