Water Heater is Heating the Engine

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   Hi
(Hanse 400 - 2006, 3JH4E, SD50)

Our water heater is heating up the entire engine when running on shore power.
Is this normal ?

Somewhere I read swabbing the hoses to the water heater would solve this, but I can't recall where I read it.

Also the overpressure value on the water heater is "leaking a bit" of water to be manually removed from water heater compartment from time to time. (not a lot but something)
Is this normal ?

Heater is a few years old. It was mounted including a non-return valve on the cold inlet pipe.

After Water Heater Change:

Before Water Heater Change:

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neo_neo Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Joined: 02 May 2022 Location: Denmark Status: Offline Points: 20	Post Options Post Reply Quote neo_neo Report Post Thanks(0) Quote Reply Topic: Water Heater is Heating the Engine Posted: 01 September 2025 at 15:44
	Hi (Hanse 400 - 2006, 3JH4E, SD50) Our water heater is heating up the entire engine when running on shore power. Is this normal ? Somewhere I read swabbing the hoses to the water heater would solve this, but I can't recall where I read it. Also the overpressure value on the water heater is "leaking a bit" of water to be manually removed from water heater compartment from time to time. (not a lot but something) Is this normal ? Heater is a few years old. It was mounted including a non-return valve on the cold inlet pipe. After Water Heater Change: Before Water Heater Change:

Captain Cook Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 23 May 2006 Location: Denmark Status: Offline Points: 1245	Post Options Post Reply Quote Captain Cook Report Post Thanks(0) Quote Reply Posted: 01 September 2025 at 21:31
	1) Heating the 4,5 liters of cooling liquid in the engine is normal. Likewise the cooling liquid is heating the 20/30 liters in the water heater when the engine is running. 2) Water is expanding when heated, so the excess volume of water is released by the pressure valve. Some owners have drilled a hole under the water heater, and mounted a tube to collect the water in a bottle/canister. In my 400, I have just drilled a hole to let the hot water disappear downwards for evaporation.
	Freya H400 #27 (2006),2-cabin, 40HP 3JH4E, 3-blade Flexofold, Aries LiftUp Windvane, Exturn 300, Jefa DD1,Simrad NX40,Icom M603(VHF)+M802(SSB)

jeb Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 05 May 2014 Location: Sweden Status: Offline Points: 339	Post Options Post Reply Quote jeb Report Post Thanks(0) Quote Reply Posted: 02 September 2025 at 10:46
	I use to have exactly the same 2 problems on my Hanse 400e from 2006 with Yanmar 3JH4. Solution: 1) Heating engine (also cools down hot water fast). I have installed a motor valve on the hose that is opening when ignition is on. An alternative is a manual valve (but remember to close/open this is not always easy) 2) I have installed a expansion tank (seaflo 0,75l) on the cold water side (i don't have a non-return valve). You need to "load" it with the right pressure. I use to have several dl of water leaking out each heating cycle and after installing this tank no leakage at all. I have attached a hose to the outlet of the safety valve (put into a bottle) just in case, but it is now totally dry. Pumps works much smother as well after this upgrade.
	Jesper Hanse 400e

Martin&Rene Members Profile Send Private Message Find Members Posts Add to Buddy List Vice Admiral Joined: 06 December 2009 Location: United Kingdom Status: Offline Points: 967	Post Options Post Reply Quote Martin&Rene Report Post Thanks(1) Quote Reply Posted: 02 September 2025 at 11:45
	The calorifier pressure relief valve is a common source of the problem generated by the expansion of the water and the resultant build up of pressure. If you put in "calorifier" in the advanced search box, "any forums, any date" you will find many threads. This is where I made some comments. https://www.myhanse.com/hot-water-boiler-dropping_topic11929_post98132.html?KW=calorifier#98132 Actually nowadays, when starting the engine or switching the water heater on, we turn off the fresh water pump, run a tap until no more water comes out and then shut the tap. We then just switch the water pump on later after the water will have been heated and when you want some water and you can leave it on, unless you have used a very large amount of hot water. The pressure increase leakage problem only arises when the water is first being heated from cold. The interesting test is to do the first bit and then when the water has been heated open the hot water tap without switching the pump on and a certain volume of water will come out demonstrating the increase in volume and pressure. On the calorifier I have put a section of small diameter plastic tubing onto the overpressure valve outlet, secured with a jubilee clip, and then taken this up to the plastimo shower outlet in the transom in which I had drilled a small hole and just secured the tube with sikaflex. So any leakage goes over the side. When I drain the system in winter, there is normally just a bit of water in this pipe and this suggests the valve is still leaking slightly, but at least it is not back into the bilges. Somebody did comment that if you are in a hard water area there is a possibility that you may scale up the PRV, but that is not a problem for us.
	Martin&Rene Hanse 341 Dipper Wheel steering, 3 cabin layout, normally based in Scotland



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