FER (Ferroli) combi boiler.sre no 0126L8129?

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