Thanks for the response.
We've got our regular engineer in.
They're very good - but right now they are foxed and so are glow worm. Hence I'm posting here.
PCB has been changed - and other things.
I was hoping someone may have experienced exactly the same thing.
One thing we have learned - if we switch the central heating off at the timer control - that is to say it totally ignores the programming - then in the morning it has not locked out. But as soon as a demand is put on the system for hot water - it locks out.
I reset it and it then works straight away.
All was well about 9 days ago - then - pow.
If anyone has experienced this - it would be great to hear what fixed it for you.
Rob (original poster).
May 2009