Weil McClain SGO-3 will not stop running. NEED HELP

Chris14

Hello all. I have a Weil McClain SGO-3 steam boiler (oil fired) that has been giving me issues the past few weeks. It started with constantly overfilling, called service tech, was told it was dirty and needed a new LWCO due to clogging. REPLACED. DIdn’t solve over filling issue. Called same service tech back, he was baffled?? After researching and reading everything came to the conclusion of a bad tankless coil. REPLACED. Overfilling issue stopped. Then it wouldn’t fire, called service tech, told it was a bad oil primary. REPLACED. Wouldn’t shut off after new primary, controlled on/off manually. Was told it was a thermostat issue. REPLACED. Got one that specifically said was used for steam boiler. Wired exactly like the old one (that was working successfully) before the issues. This boiler controls the domestic hot water and steam radiators on each floor. The radiators have their own thermostat, wired for emergency heat. That is how it was when I bought the house (June ‘19). The steam system worked efficiently and no problems the first winter. There is also a heat pump available for heat (separate thermostat). The oil primary that was replaced was bad, so I’m on my 2nd new primary and still having this issue of it constantly running until I manually shut it off. Ive only been letting it run long enough to heat up the hot water for everyday use, and on the colder days a little longer to allow the radiators to warm up the house. It’s a real inconvenience and starting to become costly with all these new parts being replaced without success. Someone recommended I post on here because you guys helped them solve their issues. The only thing left to replace is the aquastat, pressuretrol, and the oil burner itself. I would love to hear what you guys think...

Sure it’d be easier to help with all the info so here is a list of everything:
Weil McClain A/B- SGO - 7(w) series 3 [boiler]
Beckett AFG [oil burner]
Honeywell L4006A1009 [aquastat]
Honeywell R7284U1004 [primary]
Honeywell RTH6360 [Thermostat]

I think (hope) it is a wiring issue and nothing too intensive. The thermostat wire was also replaced. So the way it was previously wired was from the thermostat (R and E) to the primary ( T and T). Also on T and T was the two lines from the aquastat. When the service tech replaced the original primary, there were 5/6 separate colored wires coming from the primary. The first replacement only had 3 (orange/black/white) and he tied everything to the orange and power to black, neutrals to white. He said it was ok to do. The next primary (I ordered) came with all the separate leads for each color. So each line went color to color. The aquastat was back on T and T with the thermostat wires (R and E) again. After reading the wiring diagram it seems the aquastat is coming off the limit (red) and L1 (black). With both wiring setups the boiler still isn’t shutting itself off when reaching temp. Oddly when I take the thermostat off the wall it also still wants to call for heat?? I am at a loss mentally and the service tech doesn’t seem to have a clue and the feeling of just finding parts to replace isn’t something I can afford any further. Any suggestions/advice would be greatly appreciated! Thanks


*Also, the filter, strainer, and nozzle were replaced on the oil burner. Electrodes looked fine (service tech). New pressure gauge and pigtail off the pressuretrol. REPLACED.

Jamie Hall

If you disconnect everything from T-T, does the burner stop? Does it then start up again if you put a jumper across T-T? If so, your primary is fine.

Now it you connect the thermostat (not the aquastat) across T-T does it fire up if you call for heat? Does it stop when you turn the thermostat down? If so, your thermostat and wiring to it are OK. If not, either the thermostat has a problem or the wiring does. At the thermostat, take it off the wall, and connect the two wires together. The boiler should come on. Separate them, the boiler should turn off. If that's not the case, the wires have a problem.

Now one way or another get the boiler steaming. Disconnect everything from T-T again (the boiler should turn off) and connect the aquastat. If the boiler comes on again, either the aquastat itself has a problem or it is wired incorrectly.

Tell us what you find and we can go from there...

Chris14

THANK YOU Jamie!!
It ended up being the new thermostat that I put in. I ran through your suggestions and easily found the problem. Put the old stat back on and it is running great! I hooked the new stat up to the R and E just like the old one but it wasn’t communicating properly, I guess? Not a big deal I’m cool with the old one, and working system. Thanks again! Happy holidays

HVACNUT

E? What brand thermostat? Typical heat connections are R and W.

Chris14

Both thermostats were Honeywell’s. The new one (that didn’t work) was a RTH6360 and the old one that worked was a PRO 4000. My steam radiators are hooked up as emergency heat so that’s why it was E. (I think)

Jamie Hall

I'm glad I could help!

EBEBRATT-Ed

And @Chris14

BYW you need a new service tech. If he couldn't find that problem he is pretty weak electrically

Chris14

I agree 100%. Still undecided if I got played to fatten his pockets or if he is just not knowledgeable about his trade.