Oil boiler short cycling after adding a radiator

jamietre

I recently turned on my boiler (2002 Burnham oil fired boiler, model PV83WC-TBWN) for the first time this season. I'd taken out all the radiators in the basement during a renovation and just added one back since it's getting pretty cold down there (project not done unfortunately but need some heat!). We heat the main part of the house with wood mostly, and I haven't needed to use it at all so far this year, so this was the first time it's really run since last winter.

The boiler runs for about five minutes then shuts off for about five minutes, long before the room is up to temp. There are no errors on the oil burner, it is set to log errors. It almost seems like the burner has power disconnected from it by some other system -- the LCD display goes blank and the buttons don't do anything until the boiler starts to cycle again five minutes later. There's still power to the control board, and there's an LED illuminated showing that the thermostat is still demanding heat even when the burner is off. The pump appears to be working, there's heat at the radiator when it runs.

I think it ran for longer when I first turned it on, but I wasn't really paying attention. Will try it again after it cools down completely, but it's possible that the short cycling only occurs when it's gotten hot.

I tested the pressure on the expansion tank and it was 12 PSI, but it spewed out some water when I tested the pressure. I understand this means it has failed and needs to be replaced, so I ordered another one and a new air vent for good measure.

Questions here

1) Could the process of adding a new radiator result in short cycling, e.g. because of air in the system? There's no way to bleed this system at the baseboard radiators, and this radiator is at ground level anyway so air would rise; I figured the air venting component would take care of that.

2) I'm going to replace the tank, but is this a likely cause of short cycling? I didn't find any discussion related to this cause and effect. If this isn't likely the problem- what else should I look at?

I looked at the pressure and temperature meter on the boiler while the system was running and it doesn't appear to go excessively high on either.

Thank you for any advice.

Jamie Hall

Are you sure it's circulating? Check all the pumps to make sure that they are running. Yes, an airlock could cause poor circulation, too -- but that's a good place to start.

Just bleeding radiators won't always get all the air out. In fact, it often won't -- and if the air is causing poor circulation, it won't get to the air scoop either.

jamietre

> Are you sure it's circulating?

The temperature of the pipe at the radiator is very hot, when it had been running for a while, so I had assumed it was circulating; but I'll definitely see if I can detect operation of the pump itself.

> Just bleeding radiators won't always get all the air out

I have no way to bleed the baseboards anyway if there is could be air in the system how might I get it out?

bburd

If the operating radiator is hot through, the system is working normally. Of course the boiler will short cycle if it’s
only feeding one radiator but is sized to heat an entire house!

EdTheHeaterMan

Your boiler has a control that the thermostat is connected to. That control will send electricity to the circulator pump to move the heated water to the radiators. The same control also sends electricity to the burner primary control. that makes the oil burner make a fire safely. There is one exception to the burner electricity. If the boiler water gets too hot, the aquastat in the control will stop the electricity to the oil burner control. If the oil burner primary control is wired with only one hot wire from the limit, (B1 on your other control) the primary oil burner control just stops operating. This is normal.

If the oil burner were allowed to continue to operate until the thermostat is satisfied, the water might get so hot that the boiler will blow up from all that water getting to be 300° and making a really nasty steam explosion. I'm guessing that you don't want that to happen. No one does. When my customers asked me about this "burner off thing" you describe, I tell them that when the water gets to 180° in the boiler, and the burner shuts off... they are getting FREE HEAT, because you are still getting heat without burning any oil. And that is a good thing!

I hope this explanation helps

Mr. Ed

EBEBRATT-Ed

Sounds like it's hitting hi limit but I don't think the display should go blank.

Just clear this up how much of the house and how many radiators are you heating when the boiler is operating?

EdTheHeaterMan

EBEBRATT-Ed said:

Sounds like it's hitting hi limit but I don't think the display should go blank.

Just clear this up how much of the house and how many radiators are you heating when the boiler is operating?

If the Primary control is connected like this (left diagram) it will go blank. This is what many technicians do when replacing a 3 wire primary control on a service call. There is not enough wires from the aquastat relay to the primary control to do it as illustrated on the right diagram. And if you are busy and have 4 other no heat calls to get to... the one on the left is safe and it gets the heat on.


Mr. Ed

jamietre

Thanks everyone for the responses and detailed explanation of the way the system works! This has been very informative. I didn't realize the burner control could just be wired for a hard power off when the high limit was hit, so this seemed odd to me, but makes perfect sense now. I believe this is what's happening. (Is this bad for the primary control in the long run vs. the "full function" wiring?)

Right now this zone is hooked up to about 12 feet of 3/4" copper fin baseboard, which also happens to be pretty close to the boiler. I think the solution is that I just need to get some more radiators hooked up in the zone. This was supposed to be a stopgap because there's still work ongoing, but it seems like for the good of the boiler I should probably add some more to the zone.

JUGHNE

If you have a zone of BB upstairs, you could run that while you run your basement one, then the boiler might not go off on hi limit.