Just fitted new water valve all working fine.
On stripping old one the pin was definitely seized and filter had no mesh. Don't know how I was getting HW & CH. New stuffing box, filter and diaphragm - a good spare.
Would like to give a big 'thank you' to 831 and Bunnyman for their help. Bunnyman for suggesting problem in the first place and keeping an eye on the post, 831 for taking the time to go through the steps to rule out what it was and wasn't, namely the timer.
Discovered online parts company with exploded diagrams, close ups, part names, numbers and prices. Found it really uselful as, I am sure, other forum members would; those who don't already know of it. Would post the link but not sure about forum rules (advertising?). But, it's there if you search long enough.
Again, many thanks, ('till the next time???)
Mike