: : my gas water heater thats 5 yrs old, is not holding : : its temp. any longer. the temp. control knob is now wound to max. to get warmish water.what do i need to fix. this prob. thanks in advance. Is there any reduction in the flow rate at the hot water draw off points? There are other possible faults i.e. a sticky automatic valve reduces gas flow, general reduction in gas pressure will prevent normal heat input rates, dirt which has passed into the water inlet could reduce the efficiency of the automatic valve, do you suffer from lime scaling in the usa? Have you checked the injector for dirt? Is there sufficient gas pressure available at the heater?