Question

Hi I have a valiant mag 125 boiler, i have gas to the system as i have a pilot light but when i put the hot tap or shower on i get no hot water . what do you suggest might be the problem?? Thanks

Answer

Clearly the gas valve is not opening when you open the tap. This valve should open when there is a pressure differential across the water control diaphragm which happens when you open the tap. It is likely that the diaphragm has failed and needs replacing, our ref. 117056.