Combi problem

[gonzo]

I switched the central heating on a couple of weeks ago & it has been fine since until this morning. When I got up this morning the house was cold & when I checked the pressure at the combi it was low. I topped it up & the heating came on ok & went back off on the timer. A little while ago I tried the hot water & only got cold, checked the combi again & the pressure is down again. I also noticed that the pressure relief valve (?) has been putting out water probably because I may have overfilled the boiler. Have I got a leak in the system or could there be some other explanation. It is a Ferroli combi.

Andy.

[Set Square]

You should have a bomb-like expansion vessel somewhere in the system. Sounds like this isn't doing its job**. It *may* have a ruptured diaphragm - but more likely has just lost its air for some reason. There should be a Schrader valve (like a car tyre valve) on it to enable it to be pumped up. The air pressure when the system is cold should be about 1 bar (15-ish PSI). If water comes out when you press the button in the middle of the valve, it's had it. Otherwise re-inflate it to the correct pressure and see whether that cures your problem.

** When the system heats up, the water expands and needs to be able to do so without causing too much pressure rise. The expansion vessel allows this to happen. If this is not working, the pressure builds up and the relief valve operates - letting water out of the system. When it subsequently cools down, the water contracts and the pressure drops to below the required level, requiring it to be topped up. Vicious circle!

[Ed Sirett]

See SealedCH FAQ

[Phil Addison]

Sealed Heating System FAQ

uk.d-i-y FAQ is at NOSPAM from address to email me