Isotemp calorifier problem

[Quandary]

My boat, 2007, came fitted with a 25l. Isotemp calorifier. This is a typical piece of Italian manufacture, elegant shiny metal cylinder outside but everything is pressed from quite thin sheet. The inner tank is a stainless steel cylinder with two domed ends welded on. The outer end has an oval aperture cut in it, inside which fits a slightly larger oval domed sheet through which the immersion heater loop passes. The two plates overlap (though not enough in my opinion) and the removable inner one has a rubber (neoprene?) gasket which fits around the edge of it. To seal you tighten a single bolt through a pressed metal bridge, to pull the inner plate and gasket back against the domed cylinder end. After some time we discovered that this his joint was leaking when the system was pressurised by the pump. When the immersion heater plate was taken out the gasket was cut for about 2" around the edge of the thin plate. (Note, this is not the contact area which is away from the edge). I replaced the gasket, (about £18, but then its a marine part) at the time, I noticed that the edges of both the removable plate and the tank seemed sharp to touch so I smoothed them with abrasive paper. Oddly, the compression and seal is on the top face of the gasket, not where it is being cut at the edge of the sheet. A month or so later the tank was leaking again, I dismantled it again and found the new gasket had become cut again. As I was away cruising, I reassembled carefully and tightly (the position of the plate seemed to have become slightly displaced) which included heating the gasket with boiling water and at the same time spent another hour on the sharp edges and on trying to match the profile of the two pieces of steel sheet more exactly. It was fine at first, though we were careful not to leave the water pump on for long. However we later encountered a massive steep wake from a big fast white Coastguard tug in the Sound of Mull which nearly knocked our teeth out and now the thing is leaking again.
Before replacing it, I would attempt to try to repair it again with a new gasket, this time perhaps supplemented by a sealant: someone suggested silicone shower seal might work, if left to set for 24 hours before filling with water?
I am tempted to replace it with a 'Surecal' calorifier from the Isle of Wight, not as pretty, but not much more than half the price, is copper, with a proper heat exchanger coil, rather than just a loop, and includes a proper screw in immersion heater rather than a bit of thin plate held by a single bolt, but first would like to make another serious effort to get this leak permanently cured.
Anyone got any suggestions for a more permanent fix. Is there a sealant that might work with hot water under pressure if applied to both sides of the gasket. One that hopefully could be removed if it needs dismantling again?
Or would it be better to omit the gasket altogether and try an adhesive sealant that would ensure that the two plates can not move relative to one another?
The boat is out of warranty and I have since improved the fit and smoothed the sharp edges and I am convinced this it was a badly designed and made product but it is expensive to replace; is the Surecal better?

 

[moonshine]

PM sent

 

[Quandary]

Sealing leaks

The post must have been too long or the subject too boring and it is disappointing to learn that the problem is common with this product?
Simpler question then,
what is the best type of sealant to supplement a rubber gasket and resist hot water under pressure - Heat resisting silicone?

 

[pvb]

what is the best type of sealant to supplement a rubber gasket and resist hot water under pressure - Heat resisting silicone?

What about something like 3M's 5200? Horribly sticky stuff, but perhaps what you need. And maybe use it without the rubber gasket, let it set for 48 hrs, then tighten up the mounting bolt a bit more.

 

[Sandyman]

My advise would be to not bother trying to repair the damn thing, it will only cause you further problems. Replace it with a Surecal as you suggested.
Ive been in the plumbing/heating business for over 30 years & can tell you the market is awash with junk Italian fixtures & fittings. I avoid them like the plague. OK they may be cheaper in many cases but the future problems they cause makes them not worth the initial saving.

 

[Quandary]

Junk?

My advise would be to not bother trying to repair the damn thing, it will only cause you further problems. Replace it with a Surecal as you suggested.
Ive been in the plumbing/heating business for over 30 years & can tell you the market is awash with junk Italian fixtures & fittings. I avoid them like the plague. OK they may be cheaper in many cases but the future problems they cause makes them not worth the initial saving.

This particular Italian junk is considerably more expensive.
I would like to risk one more go at curing it before sending it for scrap, it has had less than 6 months use in the 3 years I have owned it! Part of the trouble is that it an imported product (Marathon Leisure !!!) with no back up service in the UK.
I think I may have one of their fridges too.

 

[vyv_cox]

Instant Gasket from car parts shops is perhaps the best sealant for the job. It's a silicone base plus some other compounds and is good for far higher temperatures than boiling water. However, no silicone products have high adhesive or mechanical strength, so they will not resist shearing due to poor stiffness of the calorifier joints.

I doubt if you can do much better for a sealant/adhesive with good strength than a polyurethane, of which the most available is Sikaflex 291. This will take the temperature OK, seal any gaps and also provide some strength to the joint. It has some elasticity, unlike an epoxy which would perhaps give more stiffness but crack with thermal expansion and contraction. I would try it with the gasket, provided this is a reasonable fit to the metal, which from your description it is.

 

[Quandary]

Thanks, everyone.
On the basis of your advice; I intend to take the calorifier out and bring it home, joining the cooling circuit and the hot domestic water circuit in the meantime with some short copper pipe and jubilee clips. I will have a good look at it then and decide whether to use a new gasket ot rely on sealant. I think that the cutting of the gasket by the edge of the plate, where there is no compression, may be because of the immersion loop whipping about in rough seas, causing the plate to move against the edge of the gasket; it always seems less well centred when I dismantle it than when I have put it together. This encourages me to think of trying it without the rubber gasket but just using the sealant between the mating surfaces but I will try manipulating it a bit dry first to see what happens.

 

[Bobobolinsky]

Should not be too costly to replace the immersion fitting with a screwed nozzle to fit a proper immersion element. I had a nozzle moved on a stainless tank and it cost £30 for the nozzle welded and the old hole plated over

 

[Captain]

Isotemp Water Heater

I have an Isotemp Water Heater and had the same problem. I called the USA distributor and they said there was a change in gasket materials that did not work out. They sent the new gasket and I haven't had a problem since. Gaskets can also be purchased online at isotherm-parts.com.

 

[Fmicol]

Re: Isotemp Water Heater

hello,
on my new boat i have an isotemp and find out that the engine coolant is leaking a little at the connection of tube connection and thread screwed on the water heater?I tryed to fix it but still leaking a little!!Does some body have the same probleme?What kind of product to seal the screw ?
Many thanks
François

 

[Quandary]

Re: Isotemp Water Heater

It is 9 years since I was struggling with this problem, I did try various black gooey heat resisting sealants but in the end took the good advice in post 5, consigned it to the skip and bought a Surecal. The most effective sealant I found (lasted 2 weeks rather than 1) was not one of those mentioned but a specialist tube of stuff for hot water, now long forgotten.
However none of my problems were with the engine water circuit, is that not just heat resisting rubber tubes going on to brass barbed screwed compression joints on ss tube fittings welded through the tank in to the coil? If the leak is at the weld at the tank I would be wary of a bodged repair, you dont want engine antifreeze mixing with your domestic water.
Surecal heaters do not look nearly as pretty but they are much better designed and made, just simple domestic type plumbing, the replacement was not that expensive by boating standards either.

 

[Quandary]

Sorry, read the query again, is it leaking where the hose connection is screwed to the ss tube coming out of the heater? I still have the old one somewhere, I will go and look at the way the joint is made, it may not be a compression ring.

 

[Quandary]

Problem with having space behind your garage you keep stuff that should be dumped years ago Anyway, I unscrewed the engine water connection, both are the same, it is simply a brass hose adapter fitting screwed down on to a stainless tube emerging from the heater. The joint is sealed with ordinary silicone tape (any plumbing or DIY shop) and provided this is where the leak is, you just need to undo the brass adapter, clean and check the threads, wind on fresh tape, flat and nicely overlapped, ( go in the direction of the thread) tighten up over the tape and that should cure it. If the leak is further in I would not waste any more time on it unless you have a mate who welds stainless steel.