'Twas me. The calorifier on our boat lies horizontal beneath the bed.
Both the drain and pressure relief valve empty into the bilge at the back of the boat.
The water pump takes care of the cold water system, there is then no water to drain into the calorifier.
In the picture the PRV is the red one and the drain valve for the calorifier is the white one.
Blowing down the shower tube, with the white valve open, 3 blue lines horizontal, empties the hot water circuit of all water.
TO DRAIN DOWN
Shut off valve is to the left of the water tank in the front locker in the cratch. Empty tank by leaving taps open until water runs out.
TO EMPTY CALORIFIER
Locate white wheel to left of calorifier tank. Turn this wheel until blue stripe indicator mark is in line with pipe. Open bath taps, lift shower change over valve. Remove shower head and blow down shower tube – air pressure forces water down pipe into the bilge.
Shut off stop cock in LH locker in cratch.
TO REFIL CALORIFIER
Close white wheel valve. i.e. blue stripe mark is at right angles to pipe.
Refill both tanks if empty. Open valve in front locker.
Open stop cock in LH locker in cratch.
With all taps closed run water pump until it stops. Check it does not restart – this proves there are no leaks in the system.
Open hot water tap in galley – furthest tap from calorifier, to allow “flow through and eliminate air in calorifier.
For the galley and bathroom U bends I put eco friendly antifreeze in them: