Yanmar 4JH57 water heater (calorifier) shutoff

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   Just learned this while getting my engine serviced the other day. On the Yanmar 4JH57, there is a shutoff valve for the engine to water-heater hose. This will keep the engine from heating the water in the hot water tank while the engine is running. In theory, I guess (haven’t done a test yet), this would prevent the over-pressure of the hot water tank which causes the over-pressure valve to leak into the bilge and/or the faucets to leak. The valve is a simple 90 degree shutoff easily accessed on the front of the engine. Wish I would have known that a few years ago …

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32mike Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 26 March 2020 Location: FLorida, US Status: Offline Points: 453	Post Options Post Reply Quote 32mike Report Post Thanks(0) Quote Reply Topic: Yanmar 4JH57 water heater (calorifier) shutoff Posted: 22 November 2025 at 13:21
	Just learned this while getting my engine serviced the other day. On the Yanmar 4JH57, there is a shutoff valve for the engine to water-heater hose. This will keep the engine from heating the water in the hot water tank while the engine is running. In theory, I guess (haven’t done a test yet), this would prevent the over-pressure of the hot water tank which causes the over-pressure valve to leak into the bilge and/or the faucets to leak. The valve is a simple 90 degree shutoff easily accessed on the front of the engine. Wish I would have known that a few years ago …
	Mike S/V Dulces Sueños 458 #087 Tampa, FL

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 22 November 2025 at 15:40
	Great find Mike

perry Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 13 October 2015 Location: IOW Status: Offline Points: 318	Post Options Post Reply Quote perry Report Post Thanks(0) Quote Reply Posted: 24 November 2025 at 09:13
	The overpressure blowing off the safety valve into you bildge. you need to fit a pressure accumulator in the hot water circuit this absorbes the increasing pressure [thermal expansion of water] as the calorifier heats up. The valve you indicate stops the engine cooling system hot water circulating through the calorifier. The engine coolant water is/should be a chemical mix to stop corrosion or freezing in the engine cooling system fluid should never mix with the hot water system. So yes stopping the calorifier heating by the engine will stop the water heating and expanding and the safety blow off valve wont leak, however when you turn on the electric water heater [immersion heater in UK] the water will heat, expand and blow off leak valve. I would have thought your Hanse should be already fitted with a pressure accumulator, if so it may have failed or bean set at the wrong pressure. Note I use the term pressure accumulator, other names define the same item; essentially it is a pressure vessel with a rubber diaphram with working fluid one side and pressurised gas the other. The gas side on a typical boat device can be replenished with a car tyre pump. or the pressure measured with car tyre pressure gauge. For better explanation try a manufacturers webbsite eg https//www.surejust.co.uk Perry Hanse 315 Cowes Isle of Wight UK
	Current Yacht Hanse 315 2007 Last Yacht Hanse 301 Round GB in 2017

32mike Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 26 March 2020 Location: FLorida, US Status: Offline Points: 453	Post Options Post Reply Quote 32mike Report Post Thanks(0) Quote Reply Posted: 24 November 2025 at 11:18
	Hi Perry, Yes, I understand all of that about the water heat, expansion, coolant, etc. My, and I think all of the Hanse’s of the era (2020) did not come fitted with any expansion tank from the factory, hence all of the problems and posts about leaky faucets and water in the bilge. Some have installed the expansion tank that you mention. I haven’t yet - space around the heater is at a premium with a generator installed. My previous method was to just turn off the water pump and open the hot water tap in the galley sink while motoring which works until you forget or someone needs water and forgets to return to the previous setup. Having been made aware of this shutoff valve, however, makes things quite a bit simpler. I’m just going to leave it shutoff until and unless hot water is needed at sea. It heats up fairly quickly if need be. Oh, I did test it. Ran the engine for about 15 minutes with the valve closed and, voila, no hot water. Cheers, Mike
	Mike S/V Dulces Sueños 458 #087 Tampa, FL

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 24 November 2025 at 15:39
	Yes, expansion tank story is nothing new in this forum, tons of posts here

Arcadia Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 27 November 2017 Location: Sag Harbor, USA Status: Online Points: 1112	Post Options Post Reply Quote Arcadia Report Post Thanks(0) Quote Reply Posted: 25 November 2025 at 14:53
	Just a note to 32mike. You can plumb a small expansion tank anywhere in the hot water circuit. It need not be near the hot water tank.
	Leon / ARCADIA 2018 Hanse 588 Sag Harbor, NY

32mike Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 26 March 2020 Location: FLorida, US Status: Offline Points: 453	Post Options Post Reply Quote 32mike Report Post Thanks(0) Quote Reply Posted: 25 November 2025 at 19:47
	Yeah, I figured that out and I think I found a spot under the port cabin bunk that would work. However, plumbing is not my favorite hobby! Now that I know about the cutoff switch, I think I’m just going to follow the KISS principle. Thank you anyway for the suggestion. Cheers, Mike
	Mike S/V Dulces Sueños 458 #087 Tampa, FL

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 25 November 2025 at 21:26
	It would be helpful if someone who installed the expansion tank shares the brand and size of that tank. Also it looks like it has to be air pressurized to handle pressure fluctuations in hot water circuit, which seems to me a gray area unless we have a plumbing pro who would enlighten us with some calculation (no ai bs please)

Lyn Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 04 February 2022 Location: Hampton, VA Status: Offline Points: 190	Post Options Post Reply Quote Lyn Report Post Thanks(1) Quote Reply Posted: 25 November 2025 at 22:27
	I did it on my 588. I saw elsewhere on the forum that someone used "Hot Pot". Here is a UK link: https://www.marine-engines.co.uk/product/hotpot-accumulator-expansion-tank-5-litres/ to what I bought. (Note: edit to the first post, I went with 5 ltr). I didn't take any pictures of it installed, but here is an overview. I had room available in the same area as the boiler/water heater. The unit comes with a metal strap & mount. I mounted it to the stringer in the area of the red rectangle. I chose this location so that I wouldn't have to cut into the Prineto pipe (I didn't have the tools at the time). So, I split into this area and added a T. It took a little while to find the right 1/2" Female - 1/2" Male - 3/8" Male T with a shutoff valve so that I could remove it if I ever needed, but I found one in the toilet fittings at a hardware store. For those in the US, if you put the male side on the pipe side, you can remove the NPT-BPT adapter piece. To connect to the expansion tank, I removed the supplied barb adapter and used a braided hose similar to the mixing hose you see here. The braided hose is 1/2" female thread on the tank end, and 3/8" female thread on the valve output of the T. I did encounter a challenge. The Prineto pipe is super stiff (especially when cold) and inserting the length of the T made it difficult to re-assemble, particularly since there is a nylon flat washer in there (these are BPT fittings). Since I currently use compressed air to blow out my water system at the end of the season, I disconnect the water heater and put a bypass piece in once a year. Later, when I had the Prineto fittings & tools, I cut the pipe back about 2" and installed a new 1/2" female with collar. Now, it is much easier. Edited by Lyn - 25 November 2025 at 22:49
	Jon S/V Lyn 2017 Hanse 588 \| Hull 19 \| Deep draft \| 150hp \| 220v & 110v systems \| Lithium House Bank

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 25 November 2025 at 23:09
	Thanks, really helpful And yes, Prineto is a bit of a challenge to deal with, the closest in US is PEX and some of us figured out how to connect between them. For smaller boats (mine is 458) I think 5l tank would be hard to accomodate, is there is a smaller version of it (2l something)? Any info would be much appreciated. Edited by marsella - 25 November 2025 at 23:11



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