Boiler diagnosis?

[Martin Pentreath]

OK, I have an Ariston Microgenus combi. It is dripping from the pressure-relief pipe. The system pressure is pretty high and does not go down despite the leak, which seems to suggest one of two things:

1) The filling valve it letting water through.

2) There is a leak in the secondary heat exchanger, so that mains- pressure water in the DHW side is getting into the primary circuit and and over pressurising it.

The first seems to be more probable, except that when I drain some water off to depressurise, the speed which which the pressure goes back up seems much faster than a slow leak from the filling valve would cause.

Anyway, both parts are a bit of a bugger to get to and remove, so I was trying to work out some clever trick to identify which it was likely to be before I start unbolting things unnecessarily. Any ideas from the panel?

[Roger Mills]

How much water do you have to drain off to reduce the pressure? If it's only a small amount, the pressure vessel may be shot - or may need to have its air topped up to provide greater expansion capacity.

[Ian Stirling]

Could you turn the filling valve off upstream somewhere?

[Martin Pentreath]

Hmmm, I was assuming (based on conservation-of-matter principles) that if there is a constant drip for weeks but the pressure is staying at tip-top levels then there must be new water coming in to replace the old water leaking out, pointing to one or other of the conditions I mentioned above.

[Martin Pentreath]

No, it Ts off from the same pipe that supplied the DHW going through the boiler, so I can't isolate one from the other (except by using the valve on the filling loop which is one of the suspects).

[TMC]

No, it Ts off from the same pipe that supplied the DHW going through the boiler, so I can't isolate one from the other (except by using the valve on the filling loop which is one of the suspects).

Turn off the tap at each end of the filling loop and remove the loop

Regards

[John Rumm]

Remove the hose and see...

Turn off the isolation valve at the base of the boiler where the mains cold enters.

See which of the above fix it (the latter will of course mean no hot water for the duration of the test.

That could also indicate lack of expansion space.