Troubleshooting Boiler

[Jim McGregor]

All -

First, a big thanks for this forum. It's helped me out a few times over the years.

Unfortunately, I now have a question that I'm baffled how to confront and it's time to ask for help.

I moved into home that has a boiler. Specifically a Burnham Series 2 Model B. With winter here, I have finally started to use the boiler and have run into a strange problem. When the thermostat instructs the boiler to start, either via a temporal start (e.g. be at 68 at 6am) or when I simply tell it to be at 68 all the time, sometimes the boiler won't start up.

This may occur after a full day of maintaining a certain temperature but, eventually, there is a time where the temperature drop doesn't make the boiler start back up.

It's pretty intermittent and may work for a day or more until one time it decides not to start up.

Here is what I have done so far:

1) Swapped thermostats. I have a different thermostat for the AC and was able to plug it into the heat thermostat. Same issue.
2) New battery for the thermostat (despite it not indicating it was low). Same issue.
3) Changed the thermocouple on boiler. Unsure when the last one was changed out but it certainly didn't look new. Same issue.
4) Ensured the pilot is lit during each time that the boiler should be turning on. It has been on during each time that it should be firing. Same issue.
5) Visually inspected it for debris around the pilot, etc. Not seeing anything specific sticking out other than the usual debris (dust, etc.) that you might find under a boiler in the basement.
6) Verified the pipes are reading with a pressure - they are.
7) Verified the damper is open. It's a motorized damper and it was open when I checked it (one of the times that it was running). The switch on the motor was set to leave the damper in the open position permanently.

I plan on:
1) Replacing the blocked switch vent. Apparently this piece can fail over time....

I know little about boilers as this is the first home that I've run into with one. Any thoughts or ideas would be appreciated .
Thanks!

 

[rjbphd]

Is your damper (if one) is in fully open position? Many have bypass switch on it,

 

[Sponsor]

 

[Jim McGregor]

Is your damper (if one) is in fully open position? Many have bypass switch on it,

Thanks for your reply and yes, I did - it's open. I also updated my main post as it's one of the items I checked out.

Thanks!

 

[Dana]

That's a good guess- the Burnham P-20x series boilers have dampers have an interlock switch that suppresses firing when the damper isn't fully open. During a normal burn cycle an electric motor opens the vane-type flue damper, then closes it at the end of a burn cycle. The burner controls are interlocked to not fire until the damper position is proven by the internal switch in the damper assemly. I've seen at least one in the past 10 years that was flaky due to a cold-soldered joint on the printed circuit board on the damper controls (on the side of the damper). It would operate correctly for days, then fail randomly, sometimes continuously opening & closing the damper until the power was cut. Once the problem was properly diagnosed it was easier (and cheaper) to re-flow the solder on the circuit board.