Gas boiler keeps lighting and turning off - what to do next?

cleocleo

Hoping someone has dealt with this type of issue before. I've had literally 6 different plumbers look at this boiler and no one can figure out what's wrong - always works great when they're here!

The gas boiler will light, and then immediately turn off about a second after lighting. It then tries a few seconds later to light again. This cycle continues for a few mins to 30+ mins. Other times it starts up just fine without an issue. I've seen this happen with the boiler is both cold and hot. I've never been able to get it to reproduce the issue while someone is here looking at the boiler unfortunately. Boiler has been cleaned multiple times, most of the pipes on the side of it have been replaced and the pressure cut off has also been replaced.

Here's a video of it stuck in a cycle: https://photos.app.goo.gl/463tRp9iLTZdsKyn9

Any thoughts on what I should try next? I feel like I'm just wasting money trying to get plumbers to look at it.

Jamie Hall

Couldn't get the video to play, but it is most likely something in the gas valve (not opening) or the flame sensor (not sensing the flame) or in the control. You need a competent heating contractor, preferably familiar with that boiler, not a plumber.

mattmia2

@Jamie Hall the main valve opens for about a second then closes, waits another 10 seconds or so opens, fires for a second, closes, waits another 10 seconds, then fires continuously. seems too quick for a failure to prove flane so i would guess loose wiring, bad contact in a control, bad gas valve, bad solder joint on a control board, something like that. Not sure how fast it can detect things like rollout.

A video with the cover off might give some insight if you can show what the flame is doing.

cleocleo

Here are two more videos. Just turned on the heat again, worked for about 10 mins and then started up with the issue again:

https://photos.app.goo.gl/vS6rrG67k5jco2M77
https://photos.app.goo.gl/HFx6Bh13aeneko1u6

Thanks!

mattmia2

Has anyone checked or replaced the thermocouple? It has a conventional standing pilot that is always on, right?

Edit: the pilot would go out if it were the thermocouple so it isn't that. Ses if there is 24vac st the gas valve when it isnt firing. I'm betting on a wire that is loose or a control contact that is bad.

Post a picture of the boiler and the piping around it. Is it a single zone? Does it make domestic hot water too?

kenlmad

I'm going to take a guess that it is the damper position indicator switch. It seems the damper stepper motor is just rolling right by the open position causing the burner to shut down. 10 seconds is about the time it takes the damper to normally cycle.

rick in Alaska

Damper or thermostat would be my guess. Try taking the thermostat off at the burner, and installing a jumper, and see if it works ok. If it does, then it could be a thermostat issue, or even bad wiring to the thermostat.
Rick

HVACNUT

Agree with @kenlmad .
The flue damper is not stopping at "open" and only momentarily closes the end switch.

See if there is a "manual open" switch on the damper motor.
It might be inside the cover.

Grallert

kenlmad said:

I'm going to take a guess that it is the damper position indicator switch. It seems the damper stepper motor is just rolling right by the open position causing the burner to shut down. 10 seconds is about the time it takes the damper to normally cycle.

^^^ this is my guess. There should be a switch under the cover that jumps the damper end switch. Try keeping the damper out of the equation.

Jamie Hall

That's why you guys are pros and I'm not. I didn't even think of the damper end switch.

cleocleo

Thanks everyone for the help! Once I hear the problem again I'll try bypassing the damper to see if it continues to happen (there's no switch, but a wire that can be moved to bypass)

cleocleo

I attempted to bypass the damper, didn't get it to work at first, and switched the wires back. However, after doing that problem went away for the time being. Maybe something is just loose in the damper's circuit board.

HVACNUT

What brand and model is the damper?
If the damper is locked in the open position, the end switch should be closed to continue the circuit. If not, like you said, it could be the board.
The whole assembly, damper and motor complete is easy enough to replace.

kenlmad

intermittent problems are more difficult to troubleshoot than if it failed completely. I think you are on the right trail. Good luck. Be safe.

Below are some possible problems and potential solutions, I 'll guess again that it's the first item below:

1. Bad/cracked solder joint on PCB (visual inspection on circuit board). Use magnification. I you don't have a magnifying glass, try taking a clear pic with a cell phone and then zoom in on the image. Rings around the terminal within the solder bump may be a cracked solder joint. Remedied by carefully re-flowing the solder with solder iron. Google image search "cold cracked solder joint" to get an idea what to look for.

2. Is the damper's PCB or motor loose, such that the mechanical piece on the motor shaft isn't properly displacing the position switch's armature? (I do not know your specific damper design so maybe this isn't applicable.) Simply tighten any loose screws or try superglue or JB Weld if screw holes are stripped.

3. Bad position switch, (contacts internal to part are dirty or corrode), Maybe you can remove and replace the switch provided you have some soldering skills. I do not know your specific damper design and can't provide a replacement part number.

4. Wire harness/connectors is intermittently opening the circuit. Disconnect and reconnect the connectors, sometimes this can displace any "crud' that may exist on the connector contacts. If there is crud, try to determine the source (overhead drip from drying your wet winter gloves on a hook near the boiler perhaps, like I do?) and prevent it from reoccurring.

cleocleo

Here's the damper's circuit board. I turned off the boiler, moved the blue wire of A to B and then turned the boiler back on. Boiler didn't start, so I repeated the process to move the wire back to A to make sure it still started on its own. I was going to re-test (and manually open the damper this time) but the boiler stopped cycling before I could retest. I had to pull/push on the board quite a bit to move the wire, so maybe that had an effect if there was something loose.

kenlmad

CP Number: 2677482
Description: P-EG 30 S SPDN 24V S-3
Manufactured Date: 06/03/94
Item Number: 381900322

I think it's time to buy a new damper. Yours was made during the 49th week of 1993 for your 25 year old boiler.

cleocleo

The problem has yet to return. It definitely appears the problem stemmed from the damper. Thanks all for the help!