Burnham Series 2 short cycling in a strange way

jalsa

I tried posting this earlier and it did not show up on the forum. Perhaps I messed up last time. Apologies if it is double posted. I will delete if needed.

I have a Burnham Series 2b furnace that was installed in 2003. It starts up fine and chugs along and then suddenly after about 8-10 minutes it starts short cycling. I did a much of reading and watching videos to familiarize myself with most of the components and how it should work. These are my observations:

Call for heat starts the sequence: start pamp, open damper and initiate firing sequence. The burners start fine with nice blue flame. The status light on the controller (S8610U) shows the flame current rises rapidly to about 6-8. After running for about 8-10 minutes the reading starts dropping from 6-8 to 1 over say a minute. And then it shuts off and immediately restarts. Status light shows 1 flash or none and quickly shuts down in seconds and the process repeats. I guess that is what continuous retry means.

I can keep the thermostat constant at 63F and it operates normally. The furnace comes on for about 3-5min and shuts off. The moment I try to raise it up 1-2F the furnace runs longer and the short cycling starts. It does not mattter what the starting and ending temp of water is. I did many experiments. It is just a matter of time the burner is on.
My diagnosis is that the igniter/pilot module is bad. What do you folks think or advise to check?

PS: The igniter/pilot (Honeywell Q348A), controller (S8610U) and the gas control (VR8300M) were all replaced in Feb 2021 by a heating technician. And it worked fine so far.

Big Ed_4

We would have to know what control is dropping out. You would need someone that uses an electrical meter to determine the break in circuit .

jalsa

I do have a multimeter. It does go to micro-amps. What would you suggest I measure? So far all I have done is make sure the ground is good and a few other small things. I do understand a good bit of circuits. But it will be good to know how to go about it with this furnace. So let me know what to measure. Thanks.

Big Ed_4

Burnham had problem with their pilot assemblies a few years back, the readings seem low from memory . As the boiler heats up the main burner pulls on the pilot assembly . The early models had a two wire pilot assembly ,so use the model and serial number to get the correct one ...

jalsa

The original pilot assembly was Q348A according to the manual. And the circuit diagram matches with a single wire assembly. It was replaced in Feb 2021 with the same model. Maybe I happen to have the problematic one.
I do have a replacement pilot in hand. But I have tried putting that on yet. The instructions seem straightforward. Anything I should watch out for or you think it is better to get a heating tech to do it.

Big Ed_4

When in dought , sub it out ...

jalsa

Thanks Ed.