Sunday, 25 November 2012

Pressure gauge on top of calorifier - what should it read?

Ally and Ben reported that the immersion heater no longer seemed to be doing its job. They'd been having it come on for an hour every morning. In the past this provided sufficient hot water for showers and washing up etc. Recently, though, the water hasn't been getting hot. The element makes the usual sizzling noise, as when you switch on an electric kettle, so why was it not heating the water?

Sticking out of the top of the calorifier is a pressure gauge, a red knob you turn, and a hose leading to the outside.

I think this is how it works: if the pressure of water in the calorifier exceeds a fixed limit (3 bar?) then the device allows hot water to be expelled through the hose to relieve the pressure. Is this correct?

I think you're supposed to turn the knob to "reseat" the thing, so I did, making it click a few times. Did I do the right thing? Hot water must have flowed, as the hose then felt warm.

The pressure reading was about 0.6 bar. Is this what it should be? And why is there a red needle pointing to 3 bar?

I don't seem to be any nearer finding out why the immersion heater doesn't work as it used to, unless it's something to do with the pressure. Could it be just that it's furred up? Or is it the cold weather sucking more heat out of the system?


No Direction said...

Is it a 1k heater element, ours is 1k and we run it for an hour in the morning and 1 hour late afternoon/early evening, even though the boat is warm the tank does seem to loose heat faster in the colder weather than the summer so your theory is correct. We
dont have a gauge but we do have the red adjuster, I have no idea what pressure ours is set to. Your heating element either works or it doesn't, it's only an organised short circuit, leave it on longer,
we use about 60p worth of electric a day at this time of the year.

No Direction said...

Halfie, can you move the red needle back, it looks like a "tell tale" which is pushed around by the black needle but doesn't come back so you can see what pressure was reached.

Anonymous said...

it appears to be a copper cylinder. These are approved to 1 bar ( if you are lucky. If you get it it to 3 bar, make sure your bilge pump is ok.

The pressure release valve seems to be a 3 bar unit. But it is quiet useless in this system, as it should never come to a situation where it really is needed.

Wanting higher pressure you would ned a calorifier that can take the higher pressure.

How about just changing the elemenet ? They arent too expensive.


Nev Wells said...


Have a look here...

Seems they have had a similar problem with their immersion heater - might be worth checking if it is the same problem? I put an accumulator tank on my hot water circuit to take the excess pressure that comes when the water heats up. Prior to that there was a constant drip from the relief valve into a bucket in the engine bay.

Halfie said...

Ray, yes, it may just be that they need to leave it on longer, but Ben tells me that even after it's been on for an hour, the water's not really hot enough for a shower.

I'm not on board now, so can't see if I can rotate the red needle back.

Odet, yes, I believe it is a copper cylinder. I only assumed the PRV would activate at 3 bar as that's where the gauge becomes red-lined. Isn't 1 bar atmospheric pressure? In which case the water is at less than atmospheric pressure. Is that OK? The hose connected to the PRV seems to lead outside the boat, but I think you're referring to the possibility of too high a pressure causing the calorifier to burst (a problem that Del's been addressing on Derwent 6 recently).

Is the main source of pressure in the calorifier the water pump? Or is it only from the heating of the water?

I could change the element, but I want to be sure that that is the problem. As Ray says above, it either works or it doesn't, and it makes the right noises!

Nev, I'll have a look at that link now...

Halfie said...

Nev, ooh! That looks very interesting! I didn't think about a thermostat. If A+B can survive until our next visit (around Christmas) I'll take a deeper look then.

Anonymous said...

the pressure show is the pressure thats more than the air pressure.
So if it shows 0.6 its actually has a pressure of 1 + 0.6 = 1.6.

If it would be 0,4 bar below the air pressure our calorifier now would look like a beer can a herd of elephants has walked over.

All in all 0,6 bar looks fairly ok, depending on your waterpump.
I dont know your setup, but there might me another manometer next to your waterpump. Both manometer should read more ore less the same.

And once our manometer goes above 1,0 bar your calorifier is very likely to burst. So please dont try to solve the problem by increasing the pressure.



Halfie said...

Odet, thanks for the clarification. We've not had water pressure problems, although the previous owner left us a brand new water pump to replace the original, so he must have suspected that it was on its way out. As I've said, no problems with pressure so far! When I'm next on board I'll contort myself into a position to investigate the cylinder stat. Thanks again for your help.