Help! Heater won't work at all, changed electronic card behing temp dial, changed water valve in bulkhead, flushed out heater matrix, all to no avail. The ingoing side of the valve is quite warm on both pipes, so the water must be going straight across the valve, but why not through the heater matrix. Someone suggested the water pump, but thats such a big job, timing belt etc. Has anyone experienced any similar problem?