Firebird Boiler S-90 flue overflow issue

[Adrian Lawlor]

My Firebird S-90 external Boiler overflow water pipe started overflowing constantly about 5 days ago and has not stopped since. It overflows at the same rate whether the boiler is switched on or off. I would be grateful for a clue to the possible cause.

 

[Shane007]

I think you are talking about the overflow pipe from your attic. This could be from your feed & expansion tank which may have a faulty ball valve.
It may also be from the main cold water storage tank in the attic with the same fault.

If you are talking about the pressure relief valve discharge pipe from the boiler and you have a sealed system, the issue is likely the expansion vessel is flat or ruptured. The prv could be sticking from a bit of magnetite.

Another issue could be your fill valve being left open as this could bring your system pressure above 3 bar and open the prv.