Tony
Thanks for response. I agree with you that a gas pressure problem is most likely.
I would like to check the sensor (temperature presumably). I am an electronics engineer so I should be able to do so; however I could do with some guidance on the location of the sensor, and info on what...
Our Vaillant VCW242 has suddenly developed a problem where it cannot heat up the hot water sufficiently. It normally produces hot water (I don't know the temperature but it's too hot to touch probably 60-65C) at about 9 litres/min. This morning I had to reduce the flow at the tap to 3 litres/min...