Steam Heat System Intermittent Firing

MikeC_3 · January 22

The 4 year old, single zone steam heat system in my mother's house was working without issue. The neighborhood experienced a brownout where she lost a phase. Although the boiler seemed to be connected to the working phase, it definitely was somewhat compromised. It worked well enough to provide sufficient heat but would sometime short cycle.

Power was restored, and this is when an issue arose. The boiler fires first thing in the AM when the thermostat calls for heat, then again early afternoon and then once around 8 PM. It seems to be in 6-7 hour intervals. Thermostat is calling for heat as far as I can tell (it clicks) at the programmed intervals to no avail.

My mother has a service plan and the tech showed up last night. According to her, he checked the boiler and said everything was fine. He then adjusted the thermostat and of course the boiler fired, only because it was around 8 PM. He fudged around with the thermostat and claimed it was conveniently programmed to shut off at 2 PM. That would have made for some very long, cold winter afternoons and nights the past few years.

I shut the unit down at the breaker, waited 15 minutes, brought it back online - same issue. All the lights are green and it has sufficient water. It is almost like something needs to recharge which takes around 6 hours to do so before it can fire up. Is there a solenoid or something on the electronic ignition that could cause this?

Thoughts? Thank you!!

Jamie Hall · January 22

No, the controller has no built in long term time delay. So… my thought is something got fired, and the question what. If this is a "smart" thermostat, which it sounds as though it is (programmable) the first thing I'd try is to run the boiler without it. That is, locate the T-T terminals on the controller and jump between them. The boiler should fire up normally. If it does, go to the thermostat itself and turn it up. Again, the boiler should fire up normally. If it doesn't, take the thermostat off the wall and locate the signal terminals — usually red and white — and jump between them. The boiler should fire. If it does, then the thermostat is wonky.

If, on the first test above, the boiler doesn't fire, it may be a problem in the burner controller.

MikeC_3 · January 22

The technician just left. I described the situation exactly as above. He went down the basement and within 5 minutes came back up and informed me that is was the pressuretrol. He changed the switch, blew out and reinstalled the pigtail and gauge. Everything was back working in less than 20 minutes.

He said the clue was that the unit was taking a few hours to reset. Evidently not recharge as I thought.

Any idea what was going on?

Jamie Hall · January 22

pigtail clogged

ethicalpaul · January 22

He changed what switch?

If it was the pressuretrol, that was likely unnecessary since the pressuretrol is very robust vs electrical disturbance since it itself is just a switch, electrically speaking.

MikeC_3 · January 22

He did. It is all included under the service contract and I think after the previous night's debacle, he wasn't taking any chances.

So do I understand this correctly? The pressuretrol was shutting down the system because of a high pressure reading and it would take time for it to return to normal - at that point it would fire up again when the thermostat called for heat.

ethicalpaul · January 22

Hard to say but one possibility is that the clogged pigtail allowed the increased pressure to be seen (eventually?) and then took a long time to release that pressure so until then the boiler wouldn't fire.

Steam Heat System Intermittent Firing

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