Domestic Hot Water Contaminating Cold Water

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Newbroom

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Strange problem. The Pressure Relief Valve (3 Bar) started letting by quite badly. After finally locating the calorifier hidden away behind the fridge in the galley I replaced the PRV all was fine for a couple of hours and then it stated again. Examining the system I can find no expansion tank so presumed that the pressure switch in the pump was faulty. After changing the pump for a new one exact model number the problem was cured. Till the immersion heated the water and we then had hot water from the cold taps. I have searched the system and there doesn't appear to be an expansion tank after the outlet from the calorifier or a non return valve in the supply to the calorifier.

The pump is Flo-Jet rated at 2.8 bar
The system has the pump with a cold feed to the calorifier and an accumulator on the supply line.
No evidence of this before the problem with PRV

Completely baffled

Any suggestions ????
 
Newbroom said:
Strange problem. The Pressure Relief Valve (3 Bar) started letting by quite badly. After finally locating the calorifier hidden away behind the fridge in the galley I replaced the PRV all was fine for a couple of hours and then it stated again. Examining the system I can find no expansion tank so presumed that the pressure switch in the pump was faulty. After changing the pump for a new one exact model number the problem was cured. Till the immersion heated the water and we then had hot water from the cold taps. I have searched the system and there doesn't appear to be an expansion tank after the outlet from the calorifier or a non return valve in the supply to the calorifier.

The pump is Flo-Jet rated at 2.8 bar
The system has the pump with a cold feed to the calorifier and an accumulator on the supply line.
No evidence of this before the problem with PRV

Completely baffled

Any suggestions ????
Click to expand...

It could be the non-return valve. The common position for this is where the cold water enters the calorifier. The brass fitting contains a non-return valve so that as the pressure raises in the calorifier due to the water being heated and expanding the pressure releif valve releives some of the pressure instead of the water being forced back up the cold feed, pressurising the accumulator in the cold feed, to be released the next time you open a cold tap. If you do not open a cold tap, the pressure in the cold supply (after the pump which is now acting as the one way valve) will equalise with the pressure in the calorifier then any further increase in pressure, due, say, you turning on the immersion heater, will open the pressure relief valve.

Www.solocoastalsailing.co.uk
 
Last edited:
Newbroom said:
Strange problem. The Pressure Relief Valve (3 Bar) started letting by quite badly. After finally locating the calorifier hidden away behind the fridge in the galley I replaced the PRV all was fine for a couple of hours and then it stated again. Examining the system I can find no expansion tank so presumed that the pressure switch in the pump was faulty. After changing the pump for a new one exact model number the problem was cured. Till the immersion heated the water and we then had hot water from the cold taps. I have searched the system and there doesn't appear to be an expansion tank after the outlet from the calorifier or a non return valve in the supply to the calorifier.

The pump is Flo-Jet rated at 2.8 bar
The system has the pump with a cold feed to the calorifier and an accumulator on the supply line.
No evidence of this before the problem with PRV

Completely baffled

Any suggestions ????
Click to expand...

Possibly if you have a mixer tap .......it could well be passing . Letting hot into the cold line . Your cold water supply non return sinario would lead to your cold water tank being warm / hot . If the cold tank is still cold more than likely a mixer tap ??? . Same principles as a house water system
 
Plum said:
It could be the non-return valve. The common position for this is where the cold water enters the calorifier. The brass fitting contains a non-return valve so that as the pressure raises in the calorifier due to the water being heated and expanding the pressure releif valve releives some of the pressure instead of the water being forced back up the cold feed, pressurising the accumulator in the cold feed, to be released the next time you open a cold tap. If you do not open a cold tap, the pressure in the cold supply (after the pump which is now acting as the one way valve) will equalise with the pressure in the calorifier then any further increase in pressure, due, say, you turning on the immersion heater, will open the pressure relief valve.

Www.solocoastalsailing.co.uk
Click to expand...
My calorifier was acting like a full steam boiler due to a scaled NRVv, with incorrectly positioned thermostatic mixer valve. The calorifier fully emptied itself through the cold water tap with scalding hot water. For a moment I thought the laws of physics had changed !
 
Plum said:
It could be the non-return valve. The common position for this is where the cold water enters the calorifier. The brass fitting contains a non-return valve so that as the pressure raises in the calorifier due to the water being heated and expanding the pressure releif valve releives some of the pressure instead of the water being forced back up the cold feed, pressurising the accumulator in the cold feed, to be released the next time you open a cold tap. If you do not open a cold tap, the pressure in the cold supply (after the pump which is now acting as the one way valve) will equalise with the pressure in the calorifier then any further increase in pressure, due, say, you turning on the immersion heater, will open the pressure relief valve.

Www.solocoastalsailing.co.uk
Click to expand...

Not quite sure I have my head around all of that, but practically impossible to get to the bottom of the calorifier, assuming it is a NRV problem could I add another one into the supply line before the calorifier.
 
Wilko81 said:
Possibly if you have a mixer tap .......it could well be passing . Letting hot into the cold line . Your cold water supply non return sinario would lead to your cold water tank being warm / hot . If the cold tank is still cold more than likely a mixer tap ??? . Same principles as a house water system
Click to expand...

Could this affect the whole system and wouldn't the pump need to be running.
 
You pump will run regardless if it's the hot running or the cold running . As in the whole system is of equal pressure. My boat and caravan have a single water pump . Open cold tap ring pressure drops pump runs , open hot tap pressure drops pump runs . Like u said before the system worked fine before . So no extra parts need fitting .......could well be over thinking this issue . The places I would focus are where hot water meets the cold (mixer taps ) boats and caravans don't have a ring main of water it's all just pumped to a dead leg so to speak . Try isolate each hot water output point in turn see if you can find a point where system returns to normal .
 
Thanks for you suggestions,
I am slightly sceptical of it being a mixer tap as a failure in the closed position would be very unusual but there is a blending valve on the calorifier which warrants a closer look.

What I cant quite get my head round is as the hot water expands in a normal situation does it pressurize the calorifier up to the 3 bar of the relief valve (which incidentally till it failed completely had never let by) hence the need for a non return valve in the supply. I expected to find a expansion tank.

I think I will change the blending valve and put a non return valve in the supply line and go from there. To try and isolate the supplies to each mixer tap will involve dismantling half the boat, 6 in total.
 
Newbroom said:
Thanks for you suggestions,
I am slightly sceptical of it being a mixer tap as a failure in the closed position would be very unusual but there is a blending valve on the calorifier which warrants a closer look.

What I cant quite get my head round is as the hot water expands in a normal situation does it pressurize the calorifier up to the 3 bar of the relief valve (which incidentally till it failed completely had never let by) hence the need for a non return valve in the supply. I expected to find a expansion tank.

I think I will change the blending valve and put a non return valve in the supply line and go from there. To try and isolate the supplies to each mixer tap will involve dismantling half the boat, 6 in total.
Click to expand...

As the hot water expands in the calorifier, the non return valve stops it forcing back into the cold supply. Frequent opening of any one of the hot taps will ensure no overpressure otherwise the excess blows out of the pressure releif valve. Some boats have an expansion tank in the hot system which absorbs the excess volume and avoids the pressure releif valve blowing in most situations.

Www.solocoastalsailing.co.uk
 
Newbroom said:
Quick update New accumulator cured the problem no other work required.
Click to expand...

Only just seen this, would have suggested to check pressure in accumulator , that's where the pressure goes as the water is heated, foot pump and tyre pressure gauge is needed a small accumulator would be pressured to about .2 bar ,switch pump off and relieve water pressure at a tap before checking .
 
some good info here, I was planning to investigate why I get hot water out the cold mixer tap up to the point the water pump kicks in, then it returns to cold flow.. never bothered me that much until I go clean my teeth...

and why they heck does tooth paste foam up so much with hot water compared to cold!?:confused:
 
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