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Posted: Mon Feb 20, 2017 6:18pm

Post Subject: no hot water

we cant get any hot water. there is no split in the colorifier. it doesn't give hot water to the taps. I ran the engine for 2 hours and no hot water. I have replaced the water pump because the overall water pressure was poor. this has not really improved are the 2 issues linked? if I guess it would be an air lock, but I don't know the best way to "bleed" the system. any ideas?


Posted: Mon Feb 20, 2017 7:06pm

Post Subject: no hot water

I am going to assume that you do get water to the hot taps but its cold water. Exactly what you mean by "the water pump" is not domestic water pump and the engine water pump like you have on a car, I will assume that you changed the domestic water pump. If either assumption is incorrect please get back to me. The domestic water pump might give low pressure but as long as water (cold) is flowing from the hot taps it will not effect the ability of the system to provide hot water. Unless there is a valve that needs turning on, the engine fan belt is loose/missing, the engine thermostat is stuck open, or the engine cooling system header tank is very low on coolant then the most likely problem is an airlock in that part of the engine cooling system that feeds the calorifier coil. There are two way to tackle this. The easiest as long as the pipe runs are something like sensible with no upward loops and the coolant header tank is higher than the top calorifier coil connection is to locate the feed and return pipes between engine and calorifier and find the highest joint. While keeping the header tank full of a 25% to 50% antifreeze mixture loosen and manipulate the joint until any air in the pipes exits and coolant starts to weep out. Tighten the joint and test. If that does not work try it again with the engine running at about 1200 RPM. The other method probably requires an assistant. Get a can of coolant mixture and a friend ready to top up the header tank as required. Identify and loosen the hose joint where the return form the calorifier coil connects to the engine. Start and rev the engine as above and pull the hose off the joint but put your thumb over the connection on the engine side so no coolant leaves the engine. Water should gush out of the hose but there may well be air in the pipes so wait 30 seconds or so to be sure no more air is coming out of the hose. Refit the hose, tighten and test. The above assumes that the calorifier circuit bypasses the engine thermostat. If by chance your circuit is in parallel with the skin tank then you may struggle. You may have to pinch one of the main coolant pipes from skin tank to engine at the skin tank end to prevent all the coolant missing the calorifier and passing through the skin tank. Some engines have a separate thermostat controlling the calorifier circuit. In this case a thermostat jambed closed would prevent the calorifier getting hot. It is possible that the Pressure Relief Valve (PRV) that is usually close to the calorifier on the hot domestic water outlet is leaking badly . If it is domestic water pressure would be reduced and the water in the calorifier would leak away before it got hot. To give further help I will probably need to know about your boating experience, the engien make/model and some idea about the age of the boat. You can email me directly -

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