Automatic central heating repressuriser

You must have a bit of a leak somewhere. Might be soaking the carpet somewhere or causing mould or rot.

If you leave the filling loop in place (which they deprecate) it's just a matter of opening a couple of valves to repressurise.

I’ve spent 12 years looking for the leak without luck.

After years of being sceptical of the stuff, I chucked a couple of litres of leak-sealer in my system which slowly lost pressure. Seems to have worked.

Tim

Why is/was it considered a bad idea to leave the loop in place?

It's actually a plumbed in pipe on my latest boiler, but I remember it being a removable braided hose in the past.

I suspect either the regs have changed or the addition of non-return valves makes it okay. Certainly my daughter’s boiler’s filling loop is “hard plumbed”.

Tim

I believe it's called a vented system, with automatic replenishment of water if the level drops! :-)

Any chance your system is going over pressure leading to the boiler relief valve opening?

Possibly. I’ve seen the pressure indicator go high. But how does that eventually lead to zero pressure?

Pressure relief valve only opens when the system is hot and over pressure. Once cold, the pressure can drop to zero. Usual cause is loss of expansion vessel capacity due to either failed diaphragm or other loss of air pressure in the expansion vessel.

Stick a bag or bottle on the overflow to see if water is coming out this way.

Tim

I suppose one could lash up something with a pressure reduction valve and a double check valve.

However it kind of negates some of the advantages of the sealed system; in that you can get an uncontrolled flood, and you won't be continually injecting fresh oxygenated water into the system which dilutes the inhibitor and cause more corrosion.

Checking that it is not going overpressure is worth doing. However very small leaks in pipes or radiators might not show up as a leak since the water may evaporate before it gets a chance to chow up.

Are you also getting lots of air collecting in the system? (leaks can also let air in)

One final case to consider with modern condensing boilers, is one that affected my system; and is one that it can be very hard to find. Namely a leak inside the boilers main heat exchanger, since the water will be directed straight to the condensate drain and never show up anywhere in the pipework.

See:

Again it might be possible, but it is getting more complicated.

There will be a safety pressure release value to dump a small amount of water when the pressure is too high. When the system cools down again the pressure drops but it will be lower than previously because some water has been removed. It doesn't take much loss of water to reduce the pressure and it may only be small amounts every time the boiler is run.

It may only happen, say, when thermostatic valves start closing down in your system.

How high does the pressure in you system rise to when everything has reached its final operating temperature?

As others have indicated, there may be a small leak or an expansion vessel is not working correctly.

I am not a plumber!

Modern boilers are fitted with an over pressure valve usually arranged to discharge to a safe area (can be a pipe through your outside wall terminated with a T outlet to avoid hot water being squirted at passing Cats).

Other posters have suggested tying a plastic bag over this to trap discharges.

Boilers also have a condensate drain which should run to a suitable waste outlet. Sadly, my plumbers linked the two together:-(

Your installation should include a *pressure vessel*. Basically a container with gas trapped by a flexible diaphragm. Might be built in to the boiler housing or installed separately.

The d-i-y Wiki will give chapter and verse on problems of this nature.

Yes a now dead relative of mine found a small steam vent under the floor in his airing cupboard where a joint was sor of dangling between two clips and over time had started to leak. I'd suspect this is the sort of slow leak that can cause this. In his case it was a short tighten and adding a support. Brian

So did I, until I realised there was no leak of water in the CH system, only a weeping joint in the boiler itself which was always hot and always evaporated leaving just a chalky salt residue where it couldn't be seen. TW

If the pressure gauge is faulty you won't know what it is. I had one that had to be replaced as it read 1 bar after it had been disconnected.

It is/was thought that a faulty valve, or a valve not properly closed, could lead to a leak of dirty radiator water into the drinking water.

(Mine is left in place since the Gas Man used it a couple of years ago.)

I wonder how long it will be before we can stop turning out bathroom lights with a bit of string like most other countries?)