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// http://www.surejust.co.uk" rel="nofollow - www.surejust.co.uk

Perry Hanse 315

Cowes

Isle of Wight

UK

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 

Cheers,

Mike 

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.

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.

It’s a 2 liter tank with a brand name of “SureJust” - British product. The company in the link is “Heatso” and they say they are out of Costa Mesa, Ca.

There’s also this:

https://www.supplyhouse.com/Zilmet-ZS2-Inox-Pro-Stainless-Steel-Expansion-Tank-0-53-Gal" rel="nofollow - https://www.supplyhouse.com/Zilmet-ZS2-Inox-Pro-Stainless-Steel-Expansion-Tank-0-53-Gal

This tank is “Zilmet”, 1/2 gallon from US based Supply Warehouse.

If you buy it and have luck with the install, it might give me inspiration to give it a go.

Mike

PS. Actually found Seaflo, only 0.75l, very compact and precharged with 10PSI air pressure

Under advice from Arcadia, I also added a 5 gallon accumulator to the cold water side.  Keep in mind the actual water resident in the tank is somewhere around 50% of the capacity.  Once you master a hot water expansion tank, I highly recommend it!  Hard part is finding room if you go big -- I put mine in the starboard quarter near the deck shower. Freshwater pump cycling is at a minimum & flow is smooth.

Mike

You may find this stream on expansion tanks useful ?

Lots details that helped our installation.

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 only a small volume of water will come out demonstrating the increase in volume and pressure.   With water being incompressible and the piping being thick walled, it does not take much increase in water volume to increase the pressure.

If you are interested. then there is a accumulator sizing calculator

https://www.accumulators.com/tool/accumulator-size-calculator/

If you just guess some representative values and if you just do the thermal expansion calc, then it comes out with quite small accumulator sizes.

These are the typical accumulators sold by a UK chandlers from 0.6l upwards.

https://www.force4.co.uk/department/chandlery-below-deck/pumps-water-systems/accumulator-tanks

The reference to a yacht chandler selling accumulators from 0.6l upwards, was just to answer your question as to whether accumulators smaller than 5l were available. It was not a sizing recommendation. 

People can just use the sizing calculator as a starter. 

Thanks your work and the informaton. I was aware that the pressures go high [somewhat dependant on the stiffness of plumbing etc] without a accumulator in the circuit, but seeing your gauge at close to 100 psi reinforces my theory that the  isotherm vitreous lined calorifiers are prone to fail early; not to mention the poor quality of the isotherm pressue release valve? With pressure expansion of the pressure vessel and the brittle vitreous coating cracking. Either way the quality alternatives of a copper [Surejust UK] or Duplex SS pressure vessel is a better solution, and of course a pressure accumulator to limit the peak pressures.

Perry