I have done a search here and done as much reading as I can, and am a bit stuck/unsure how to proceed.
About 5 years ago, a Williamson-Thermoflo GWA 105 boiler was installed for this 1940s vintage 1000 square foot house with hot water baseboard. The house is poorly insulated. Prior to conversion to gas, the old oil boiler was able to heat the house. The unit was heating contractor installed.
The "new" gas system performs ok when the outside temperatures aren't too bad, i.e. above freezing. But when it is sub freezing, as it is now in the Northeast, the heating system cannot keep up, to the point that we've got cold fingers and are dressed for the outdoors, indoors. The boiler has "functioned" this way on the coldest of days more or less since installation, and I think it has to do with the boiler itself. Original heating contractor's service department failed at figuring the problem out long ago.
The boiler setpoint is at 180 deg F. The Economy knob is set to min, because we have trouble keeping heat in the house.
When the outside temperature isn't too cold, the boiler fires up and heats water to 180 deg F, cuts out and lets the circulator pump the hot water until supply temperature drops to 140 deg F, then fires up again. That is, it seems to operate as it should when the heat load is minimal.
When the outside temperature is cold, as it is now (18 deg F now, single digits in the last couple of days), the boiler fires up at seemingly random water temperatures, and maybe heats to the setpoint but more likely doesn't. It will frequently get stuck in something I call limp mode, running between 120 to 140 F. Often it short cycles, firing up but then shutting off immediately or close to it. Thats not enough to get this place out of the lower 50s. I have tried setting the setpoint lower, setting it higher, but it doesn't seem to help.
Tstat is an old Honeywell set high enough that the call for heat LED on the boiler is always lit, and the circulator always pumping.
If I baby-sit the boiler during limp mode, I can crank the setpoint one way or another to cause the limit circuit to be met, and get the boiler to start, though it might or might not get to the setpoint without repeating this a few times. Sometimes it will seem to work for a while, (operating above 140 deg F is what I mean by work), but if you stop watching it, it misbehaves.
Last year or so we had a heating tech from a different company than the original installer come out. He was kind of stumped and threw a temp sensor at it, though I don't think the temp sensor resistance values were out of range per the manual and pointed that out to him. Of course after he replaced it anyway as a first step; we had mild weather so it seemed to be working fine, until the next cold snap, when it didn't.
Now we've got prolonged cold weather and the boiler's having trouble keeping it 50 degrees in here. I have checked the resistance values of the temp sensor and they jive with what the manual says.
There are no flashing LEDs on the controller.
For brief troubleshooting purposes only, I also did the following for long enough to eliminate these components as the cause of the problem:
* jumpered the Spill switch. Problem continued, so re-established as-found connection to spill switch to preserve function of this important safety device. I has guessed this part might be the cause, as the chimney doesn't have a cap.
* jumpered the rollout switch. Problem continued, so re-established as-found connection to rollout switch to preserve function of this important safety device.
So, according to the trouble shooting flowchart of the manual, the next thing to replace is the controller, p/n 381-330-014WT, the Model # 1135-601 controller. So far, the only quasi-local place I have found to have it, won't sell it to me because I am a private party and not a mechanical contractor. But it's cold, and the place I think will have it and sell it to me has a constant busy signal, probably because they are wicked busy. And most searches online list it as "discontinued", though I think I may have found one place that has it.
Does anyone have some guidance for me? I'm just about ready to take a gamble on buying the controller online, but I thought I would look for a little wisdom before I do something like this. Money's tight, but we are cold.
Thanks in advance, and sorry for the long-winded post but I am trying to relay as much info as I can.