by Jimmimac »
Thu Jan 13, 2011 3:07 pm
You need to locate the central heating header tank, not the hot water header tank, mentioned by the poster above. They are different (unless you live in a very old property with a crude direct system; highly unlikely).
The CH header tank is usually only quite small (holding about 5 gallons/25 litres); the HW header is much larger.. so if you find two header tanks, the smaller one is for the CH.
Have you tried tracing where the overflow pipe goes to? If it comes out of the house wall, or out of the fascia board (just under the guttering), then try to work out where it comes into the house/loft, find it inside and then trace it back. It must end at the tank!
When you do find it, the likelihood is that the ball valve will be stuck full-open. Give it a waggle and it will very likely close and then operate correctly. Because these valves operate so infrequently, when fitted to a CH header, they often get sticky. Other possible causes are: float ball dropped off the end of the arm (it happens!); float ball damaged/puntured (so it no longer floats!); washer/seal at water input damaged; worn valve housing leading to sticking valve spool. If there is doubt, the quickest is usually to buy a complete new float valve assembly and change it. You may need to adjust the water level after fitting the new valve, which is pretty straightforward.
The CH header thank only needs to be about half full.. just so long as the outlet is covered to a depth of a few inches all will be fine.
Good luck.