Since taking the 3way valve off my combi boiler to change the diaphragm the domestic hotwater is not switching on but the central heating is coming on when swiched on so obviously some error has been made putting it back together, would it be possible to get a break down diagram of it so i can rectify the problem?

STEVEN GUTSELL, April 2006

This is def something to do with the valve. As Andy advised put your hand round the back of the valve to feel the pin, it should have 1/2" plastic disc on the end that pushes the micro switch when the rubbers inflate with water. They are very fragile, I have had a brand new one break on me. If the disc is ok then it is def something to do with the rubbers - even though they are new you may have pierced them in putting them in & they aren't inflating. Try turing the hot tap onto full blast from closed to see if the pressure temporarily fills the diaphram & presses the switch to fire up. If there is a hole in the rubbers it will switch off as the pressure drops. It should only take a 1/4 turn on the tap to switch if the pressure is ok - this is a good indicator the rubbers have gone. The cetral heating will work because the valve is in the default position & doesn't need to switch over like DHW needs. Lee.

Lee, May 2006

check that the little black disc is fitted on the end of the spindle that pokes out, this will push on the microswitch buttons to bring the hot water on.

andy, April 2006