Best Of

See, you dont want to fix it. Its a hobby. A wet rotor circulator should've gone in 6 days ago. And no heat the whole time? If the place is vacant, or there's another heat source, ok. But if the place is occupied with no alternate heat source... why?

The question I would start with is, has it ever worked satisfactorily? If the answer is yes, let's focus on what has changed since it last worked. If no, that's a little trickier, we're looking at some sort of design issue.

The heat output of a radiator is given by the flow times the temperature drop. If the heat output is less than what is wanted, either the flow or the temperature drop has to increase. Generally, to increase the temperature drop you have to increase the water temperature.

If it worked at one time, my first suspicion would be flow has become diverted or obstructed. I would make sure the system was free of air before checking anything else.

@Pumpguy You have to be cautious about returns in the furnace room. They (inspectors) don't usually go for that as it can mess with the combustion air

@EdTheHeaterMan

Sky hook?

F09 was a common problem with older Munchkins. Replacing the control board with the upgraded 926 board (part #7250P-731) usually resolves the problem.

I order mine from Jupiter Heating. Once you place the order, email them the model and serial number of the boiler so that they can program the board for your unit.

https://www.jupiterheating.com/htp/parts/7250P-731.html

what is the purpose of the rest of the piping on that mix loop? there are two tees and the supply continues out as well, is there more than one zone on that line? if so that lower pump is probably setup to energize when the mix circuit calls, that lower pump doesn't need to run at all when the mix loop is calling