If your boiler heats the rads ok then it's not faulty! Most likely there is a fault in the heating controls instead - the usual culprit being the 3-way valve (usually found in airing cupd) - its probably stuck in the heating position - it needs to be in the closed posn to do the hot water. REpair of this valve can be DIY - try changing the motor first if this doesnt work then replace whole actuator or ewven the whole valve if it is seized. BEWARE 240volts inside so must isolate first !!!
Gas58man, March 2012
