3yr old fisher paykel dishwasher not hot.

Question

Hi, my 3yr old f&p dishwasher is only getting hot some of the time. It averages about 1 in 3 washes where it actually gets hot and cleans properly. We have tried all of the obvious things like clearing the drain and cleaning out the squirter bars. It seems to respond well to adding a little bit of disinfectant in with the tablet but it may just be coincidence. The machine is plumbed in to the cold water supply. The water supply is hard water supplemented with rain water in the winter months. Any ideas for a fix? I thought it may be a poor connection on the heater element?