C/H working ok. Hot water temperature is not regulating and gets dangerously hot.
Termister is clean and checks out ok when tested in cool/hot water. What voltages shoud be seen at the Modureg valve as the water temp increases from cold to hot?
If I can check this it can be worked out which is faulty, the valve or the control card.
Any help with this problem will be much appreciated

Bryan Wilkes, May 2008

when u say the water is not regulating, does it only get too hot or alternate between hot and cold?

a fluctuating temp would indicare a problem with the plate heat exchanger (mostly sludged/scaled)

I would just change the thermister for new first (sometimes they can go out of calibration)

whats the water flow like (measure with a weir gauge & temp gauge) have you checked the in-line water filter is clean and unobstructed?

If the ch is working fine i can hardly imagine it is the gas valve, and also unlikely to be the pcb (but stranger things have happened!)

work out your flow rate and delta-t temp, check filters and measure temp on the dhw flow pipe against the thermister see what ur getting...compare to manufacturers instructions

T, May 2008