Heating System Leak

[RoryC]

Hi there,

I hope someone can help me with this. I'm having difficulty with my heating system. Basically, I had the gas guy in recently to service the bolier and he discovered that my pressure was down at zero bar so he filled up the system to 1.5 bar from the mains as it is a closed system. After about a day the gauge was down to zero again.

I filled it up again and the same thing. The gas bolier just cuts out when I put it on, due to the fact that there's no water in the system I suppose. There is no evidence of a leak anywhere in the house so I am guessing that there is a leak under the living room floor (which is concrete). Has anybody any suggestions. They would be much appreciated.

Regards, Rory.

[The Natural Philosopher]

You do get a bit of loss due to outgassing..bleed and repressurise until it settles down.

[Aidan]

Defective pressure relief valve? Check 15mm discharge pipe going to outside after refilling, whilst boiler warms up.

No air in the expansion vessel? Did gas man check this?

[Roger Mills]

It's very likely that the pressure vessel is either duff or has lost its charge pressure. The result is that, when the system heats up and the water expands, it has nowhere to go - so discharges through the pressure relief valve. When it cools down you have zero pressure.

Check the charge pressure in the pressure vessel with the water system depressurised. You need a car tyre pressure gauge to do this. The pressure should be about 0.7 bar (10 PSI). If it's low, pump air in with a car foot pump, operated by hand. Then re-pressurise the water system to 1 bar using the filling loop.

This may fix the problem. If it doesn't, it suggests either that the pressure vessel is completely duff and needs to be replaced, or that the pressure relief valve is faulty. Find the outside pipe through which water discharges when the relief valve operates, and hang a jam jar under it to see whether any water comes out.

[Aidan]

Strange that the water leak wasn't bad enough to cause the boiler to lock out before his visit. Or was it?

Did he drain the system, for example to check & re-plenish the air charge in the expansion vessel? If so, did he connect a hose to drain it, or did he drain it by operating the pressure relief valve easing lever/knob?

[Ed Sirett]

Everything you need to know and then some is in the Sealed CH FAQ. You probably have a failed expansion vessel.