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Loss of pressure on Combi boiler

Bloom77 Member Posts: 2
I have a aqua balance, 155,000 combo boiler. Installed by a contractor two years ago. It was working fine until a month ago when he came out to do annual maintenance. He cleaned it with vinegar by running it through the system with a pump. After he finished the boiler every day, usually at night will shut off and the error  code 37 shows up - less than 8 psi. I can start the system easily by shutting off the switch and turning it back on.  It resets and works fine for 4 to 12 hours. I’ve had the contractor back and he cannot figure out what’s going on. He replaced the air scoop and the fill valve and said they were full of sediment but the problem persists. Any ideas?  Why was it working fine until he cleaned it with vinegar and water? Any connection? he thinks it has something to do with that I’m on well but I have a good pressure going into the waterline from the pump and air tank.


  • Bloom77
    Bloom77 Member Posts: 2
    I forgot to add that when the error code 37 comes on I get no domestic hot water until I reset the unit.
  • Jamie Hall
    Jamie Hall Member Posts: 23,524
    Has nothing to do with the well. Forget that.

    Try this. Manually bring the pressure up to 15 psi cold, and then close the shutoff valve from you domestic water to the boiler -- there must be one, though I don't see it. Then wait. The pressure should hold at that cold, and should rise some when hot, and then drop back down to that cold. If that works, there's a problem with the fill valve (I don't see a backflow preventer either, which is not right).

    If the pressure doesn't hold or return, then begin looking for leaks...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • oreo123
    oreo123 Member Posts: 48
    Me I would do this - I would wait till its off for a few hours after being locked out. I would put a hose bib pressure gauge on it to see what the pressure is to verify the boiler pressure gauge is correct. If its under the manufacturer's whatever p.s.i. then the low water cutoff is doing its job.

    If its around the cutoff pressure I would manually fill it to 12 psi *when cold* assuming that this is a one or two story house with boiler in the basement.

    Then I would put the heat and hot water on.

    As the temp rises in a boiler so does the pressure. If the pressure was already low to start with at nightime when the heat goes lower and there is no hot water used - the pressure will drop. If the pressure was set too low to begin with there is the error code in the middle of the night.