Baxi Boiler Pressure Relief valve

[John Rumm]

You should not need to turn the heating off just to remove the loop. There will typically be a tap at both ends (or sometimes just a tap at one end and a non return valve at the far end). Its purpose is just to add water to the system. Normally it should be completely off. The purpose of actually removing (at least one end of) the hose is just to check that the taps are not letting by. If they are, then that could explain the apparent rise in pressure.

Another possibility is the that the pressure gauge itself does not work correctly any more. (I met one of those the other day when I helped a friend remove a rad and tweak some CH pipework - when I went to re-pressurise the gauge seemed stuck on about 1/4 bar and would not budge)

Expansion chamber issues are usually when it does not handle expansion correctly - so you would expect to see the pressure shoot up when the system heats. That quite often results in the PRV letting go, and then the system may have insufficient pressure to restart the following day when starting from properly cold.

Its quite common for one rad in particular to acquire most of the air that comes out of the system. You also normally can bleed more out of it some time having fully bled it a week before - again as more dissolved air comes out of the water over time.

[AnthonyL]

Yes I see how it works. The one on the mains side which is the one I use to re-pressurise has broken its plastic handle so I need a spanner to rotate the square. The other end is an inline tap/valve (don't know which) which requires a screwdriver, presumably to turn 90deg. It probably hasn't been turned off since install and the fittings not removed since install. Knowing me water will leak and I'll not get the fittings securely back on. Anyhow since bleeding the pressure has remained satisfactory.

The gauge is fine. It responds immediately to any bleeding or repressurising and goes now from 1.0 when cold to 1.5 when working.

Right I'll keep doing this one. All the others immediately let out water, this splutters. The bleed valves are on the back side not on the edge. Messy even with a sponge and a little plastic bowl.

Does it matter whether bleeding is done cold with no pump or when operating normally?

And would air upset the pressure and/or the pump?

[John Rumm]

If the second valve is actually a tap, then you would need to turn it off before removing the filling loop anyway. (if it is (or has) a non return valve then it should stay water tight, and you would be able to remove the loop regardless of the tap position)

Its usually better to do cold (less chance of scalding yourself, or confusing the pressure detection in the boiler)

The pump, not really unless there is a very significant amount of air. The pressure will drop a bit with bleeding. After a couple of bleedings there will be progressively less each time anyway (so long as its not gas from corrosion that's accumulating). A small amount of air in one rad is not really a problem if its still getting warm enough.