Right thanks for the advise, checked gas flow against one in manual too much gas, gas consumption in manual states 2.82 m3/h. Never thought to check if things had been twiddled
As far as the water supply goes that is fine. British Gas checked the flow rate whilst they were trying to flog me a new boiler for £2500 fitted and an easy one "straight swap"(his words) to boot.
If the thermistor has gone would this not account for the too much gas bit as it wouldn't know...
I have a Vaillant VCW 242EH and for a while now i have been putting up with the problem of the domestic hot water supply being just too hot, it is unbearably so. I have set the temperature selecter valve to the lowest setting (still boiling hot). I did increase it to the three setting to check...