Thanks Gary. Pity i have to drain buts thats life.
There are 9 radiators upstairs. How will i know how much to drain out at the boiler? To refill the system i will have to turn on a tap until the pressure reaches the current level and bleed the radiators as you say. How can i put rust inhibiter into such a system?
The downstairs has underfloor heating so i assume that is separate from the water in the radiators. The plumber who fitted 4 such valves upstairs in 2006 drained the system and the underfloor system did not appear to be affected.
Vincent
September 2008