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Oil Boiler Leaking Water

DB77 Member Posts: 2
My oil boiler is leaking water.

I have water leaking from the pressure relief valve at a pretty steady

pace. It fills up a large mop bucket in about 2-3 days time.

The expansion tank on the oil boiler was mounted sideways rather than

vertically. It is unsupported and is sagging. However when the near side

of the tank (what would be top if mounted vertically) is hot while the

far side (what would be bottom if mounted vertically) is cool and it

does sound like there is air in the tank when performing the knock test.

This seems to indicate a working expansion tank. Does this mean that

the expansion tank is not likely the cause of the PRV leaking?

Another symptom is that the system always seems to have zero pressure

according to the boiler pressure guage. I believe the pressure guage is

working because if I hold the pressure valve open I can see the pressure

increasing on the guage.

Any ideas on what might be causing the leaking and zero pressure?

Thanks guys


  • Paul48
    Paul48 Member Posts: 4,469

    Replace the PRV.Sometimes when they discharge, they will not seal afterwards. Replace and properly mount the expansion tank. Is there a coil for domestic hot water in the boiler?
  • billtwocase
    billtwocase Member Posts: 2,385
    agree with Paul

    sounds like a water logged extrol, lazy feed valve
  • northernboiler
    northernboiler Member Posts: 55
    I agree but would go one further..

    I would replace what I like to call the "holy trinity"

    Replace the water feeder, expansion tank & PRV.

    The water feeder is not operating properly anymore if you have to manually open it to add water. The diaphragm in the expansion tank is most likely blown due to over pressurization The relief valve is probably not seating correctly anymore from it weeping so long or too many times.

    In my experience, a situation like this is like a chain reaction, the water feeder goes bad, it ends up blowing the expansion tank, and then to relieve the built of pressure in the system, the PRV "weeps". And with correct pressure or not in the boiler, doesn't stop leaking.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    And with correct pressure or not in the boiler, doesn't stop leaking.

    I bet it will stop leaking after a while, when the calcium deposits build up and seal it off.

    Then, when the aquastat sitcks on, the excitement will start. Call in the mythbusters.

This discussion has been closed.