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Bryant 234B Boiler pressure trouble

Alan_11 Member Posts: 64
I agree with Bruce, but it sounds like the expansion tank needs to be drained or replaced.Bring the pressure down to 15 lbs. and then run the heat for a while ,if it starts moving towards 30 lbs. it's probably the tank.


  • R.S. West
    R.S. West Member Posts: 3
    Bryant Boiler Pressure trouble

    I have a older Bryant MD#234B-5RW 128,000 BTU output water system. Installed in a 900 sq ft single family home. Water has been leaking out of pressure relief valve. I have done the following. Replaced pressure reducer, air bleeder at boiler expantion tank and pressure relief. Still i have trouble. The aquastat starts at 180 deg and goes well into the 200 deg range. I start to leak water at 180 deg @ apox 35-40 psi. It seems if i were to run at apox 140-160 deg i wouldn't have a problem?? Do you think this stat is over ranged for this boiler?? All baseboard heaters have been bleed of air. For now i have throttled back on gas supply to burners which seems to help control this problem somewhat. I have also checked my gas pressure which was at 3.5" Not sure what to do next. Thanks,
  • bruce_21
    bruce_21 Member Posts: 241

    The pressure relief valve is doing its job. It is supposed to let go at 30 psi. The problem is too much water in the boiler. In a one story house the pressure never needs to be more than 12psi to keep water in the radiators, so with 12psi when cold it shouldn't go above maybe 20 when heated. I suspect you've got the system overfilled with water somehow. Try bleeding off some water until the pressure goes down to something under 20 if the system is hot. Watch the guage for a while, if it starts going up, the filll valve, which you said is new has a problem. It should be factory set at 12 psi. Maybe some crud got into it or the setting was changed or the "fast fill" lever is raised.
  • Chas_3
    Chas_3 Member Posts: 3
    Too Hot

    I think your aquastat is borked and is not shutting down. Keep the temps BELOW 190, over that and your pressure will increase. Perhaps you need a new guage too.
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