I have just replaced the diaphram in the Diverter valve, but still have very low pressure and no running water from the dhw taps. The pilot light will ignite. The super 90 boiler is 7 yrs old.
The cold water pressure is ok.

Adrian Ineson, October 2007

There is a funny sized pipe (about 13mm) on the left side of the calorifier (big cylindrical thing in the back of the boiler) this is the DHW outlet pipe, its very common for this to become full of limescale deposits. remove the pipe from the boiler (a bit of a pain). and give it a tap with a hammer or a slight crunch with some pliers but dont damage the pipe, this should loosen the deposits. Don't cut or damage the pipe as its not a standard size and quite hard to come by.

BG steve, October 2007