I have a weird problem. My boat has a Ford engine and an Alde central heating boiler feeding a twin coil calorifier, but neither heats the water.
Both supplies appear to be flowing correctly and both sides of the calorifier coils are hot, but I only get cold water out of the system. The only odd thing is that I had to fit a non-return valve because it was back-heating to the cold tank at first. Could it be a weird air lock? TONY REPLIES... This makes no sense – are you sure you are waiting at least an hour from cold before trying to draw off hot domestic water?
Initially, the pipes going in from the Alde or engine should be cold and then get hot as the engine/boiler heats up. At that stage, the return pipe for whichever is producing the heat should be cooler than the inlet because the domestic water has drawn heat from the relevant coil. When the calorifier is up to temperature, both pipes should be hot or very hot.
I wonder whether you have a horizontal calorifier that is not orientated correctly so the hot domestic outlet union is not at the top. Also, do you have a thermostatic mixing valve to the domestic outlet that is either malfunctioning or incorrectly connected, some calorifiers have one as standard?