Emersion Heater puzzle

[Tranquillow]

I recently fitted a new emersion heater to the calorifier of my boat as it didn't have one from new. The only problem is that the overheating cut-out keeps popping out. At first I thought it was something faulty with the emersion heater itself but then realised that it does not pop out when in operation under shore power but pops out when NOT in use but after the engine has been running. On closer inspection, I noted that the cut-out is set to 80 degrees and having read the engine manual, I note the the engine thermostat is rated at 85-95 degrees. Hence, it is the engine hot water circulation which is causing the cut-out to pop. Now, what should I do? the emersion heater leaflet and label says do not alter the setting of the cut-out from 80. (it only goes up to 85 anyway). Do I therefore disconnect the cut-out from the circuit altogether? There is a standard thermostat in circuit still, so the shore power to the heater will be controlled by that but there'd be no back-up. The engine cooling system is pressurised, so it won't boil even if the calorifier does. Any other ideas would be most welcome!

 

[PoRL9]

Do not, whatever you do, disable it. On "boat power", you know there's an upper limit as to how hot the water can get. On "shore power" however, if the thermostat fails, then the water will just get hotter and hotter, and - assuming you have a sealed boiler - you will end up with what is normally referred to as a "bomb".

AFAIK, your only options are a) to fit a second tank solely for "shore power" hot water, or b) Keep resetting it (although I'd be really interested if anybody else has suggestions)

 

[ProDave]

Don't bypass the safety cutout. If you do, and the main electric thermostat fails, then when heating on shore power it WILL boil the water. Lets just hope if that happens you have a pressure relief valve.

The only solution I can think of is fit an engine thermostat with a lower temperature, that's if one is available. Or just accept you have to reset the trip each time you want to heat water by electricity.

 

[Tranquillow]

Emersion Heater Puzzle

Thanks Guys.

Resetting each time is a bit of a fag as I have to climb through the cockpit locker(have to empty it first) to get to it, then take the red cap off (pliars and screwdriver needed) so as to press the button in and all this in the dark!

I can't see any pressure release valve on the calorifier but I guess that would be an alternative. Perhaps I could fit one onto the top hose (hot water take-off).

Anyone know if there is such a gismo?

 

[KevB]

I think it's 'standard procedure' to bypass the internal cutout when fitted to boats. I just so happens that a neighbour on my pontoon has just had a new one fitted by a marine company and they did just that.

I should add he does have a pressure release valve...

 

[ProDave]

A pressure relief valve on a sealed, pressurised system is not an optional extra, but an essential safety device.

And lets be clear, you should not bypass the electric thermostat and then rely on a pressure relief valve to stop the bomb exploding when the water boils.

To make getting at it easier, replace the standard hex nut with a wing nut. Then at least you won't need tools to take the cover off and reset the 'stat.

 

[KevB]

Another 'safer' option would be to buy one of THESE and put it in line between engine hot water feed and hot water tank. Adjust so tank doesn't get hot enough for cut out to pop out.

 

[snowleopard]

One question - do you have a thermostatic mixer valve on the take-off from the cylinder? I ask because domestic hot water at 85°C is dangerously hot. The alternative is a thermostatic bypass to prevent the water getting above 65° when being heated by the engine. If you had that the problem wouldn't arise.

 

[Tranquillow]

KevB, That's brilliant! Thanks very much. I will fit one. The hot water is far too hot after a bit of motoring, so this will cut down the A & E visits for Mrs Tranquillow!

 

[snowleopard]

You must provide a bypass so that when the flow through the calorifier is cut off water still circulates through the engine, otherwise the engine will boil.

 

[V1701]

Immersion

.

 

[jon711]

Just a thought, and not too sure how practicle.

Fit a bigger flow engine cooling pump so that the temperature does not exceed the limit, most cooling pumps have similar templates, so a larger one should fit...

Jon