Thanks Chris, sorry about the model, its a Turbomax Plus 824 E (with digital display) Also there is a mention on the name plate of VUW GB 242-5 if that means anything to you. The boiler is about 3 years old, and the problem was there last year but only very occasionally. This year its much more...
I have a Valiant Turbomax plus 82X E that has developed a problem in that it does not always switch between hot water and CH. If the CH has turned off for the day, and then I try and run the hot water it runs cold, or visa versa. I can temporary fix this by switching off the boiler and back on...