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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 2804
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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my feed and expansion tank is overflowing. It is not a leaking

Customer Question

my feed and expansion tank is overflowing. It is not a leaking ball cock valve and i have eliminated a leaking hot water cylinder coil pipe. The excess water causing this overflow is coming from the vent pipe.
Submitted: 3 years ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 3 years ago.
Hi my name is XXXXX XXXXX lets see if we can get you sorted in the shortest possible time. Puzzling, as the excess water must be coming from somewhere. Have you tried to turn off the supply to the tank and see whether it still goes up? How close to the overflow level is the existing tank water level?
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 2804
Experience: Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
Andrew Smith and other UK Plumbing Specialists are ready to help you
Customer: replied 3 years ago.
Hi Andrew
I have tried shutting off the supply but it makes no difference. The difference between the overflow level and the normal level is approx 7 inches.
Expert:  Andrew Smith replied 3 years ago.
Even if you shut the supply off to the central heating tank and leave it off - it still goes up? The water MUST be coming from somewhere else, even if you were pumping over the top of the tank it would not affect the water level once the pump was off and it would go back to the original water level. You say you have ruled out a pin-holed cylinder coil?
Customer: replied 3 years ago.
I thought you meant shut off the supply to the expansion tank.Which tank do you mean?
I have shut the supply to the expansion tank and the cold water supply tank and left them overnight,and there was no difference in the levels in the morning.
Expert:  Andrew Smith replied 3 years ago.
OK, so it only overflows when the boiler has been on for some time. Can you turn off the supply to the central heating tank only and run it for a couple of days and then come back to me. If the water has gone up then, there will be water getting into the central heating from somewhere else.
Customer: replied 3 years ago.
I'm unsure what you mean by the central heating tank. Which tank is that? Is that what you term the expansion tank?
Expert:  Andrew Smith replied 3 years ago.
Yes it is the expansion tank for the central heating - the small one. The bigger one is the cold feed tank for the hot water cylinder.
Customer: replied 3 years ago.
Ok. I agree if the level does go up then water must be added somehow.
I'll be in touch
Many thanks
Geoff
Expert:  Andrew Smith replied 3 years ago.
Thanks
Customer: replied 3 years ago.

Hi Andrew

I have completed the experiment of closing off the supply to the 'Central Heating Tank' and the water level has still increased. I have watched the water overflow through the vent pipe and estimate it to be approx 1/8 to 1/4 a cup full every 1/4 hr.

I can but think this extra water can only come from one source, ie, the hot water cylinder but as I mentioned I did conduct the known test of isolating the supplies to both expansion and feed tanks and measuring the difference overnight (there was none). Are there other tests or should I be looking at something else?

 

Geoff

Expert:  Andrew Smith replied 3 years ago.
Unless you have somewhere in your house where the 2 waters meet? It is not a combination boiler on an open vented system?
Customer: replied 3 years ago.
No it is a open vented central heating system supplied by a standard boiler. Do you know of any other test for cylinder leakage?
Geoff
Expert:  Andrew Smith replied 3 years ago.
You could turn off the supply to the hot water and open the hot tap until it stops, then turn the tap off again. Leave it until the morning and then try your hot tap again. If you have water there you will definitely need to replace your cylinder - this means that heating water (with chemicals in) is mixing with your hot water!
Customer: replied 3 years ago.
Thanks Andrew I'll try that tonight.
Expert:  Andrew Smith replied 3 years ago.
Let me know
Customer: replied 3 years ago.
Didn't manage it last night but will try tonight - I'll let you know the outcome

Geoff
Expert:  Andrew Smith replied 3 years ago.
OK
Customer: replied 3 years ago.
Hi Andrew
Well, I turned on the hot taps today and there was only a small amount of water coming out. Does this mean there is a small leak? There was no appreciable difference in the level of the expansion tank.
Just a point of clarification if you would please - I closed the cold water supply to the hot water cylinder,this meant the hot water cylinder did not empty, although the hot water taps did empty - was this ok, or should I have emptied the cylinder by shutting off the cold water supply to the cold water feed tank.
Expert:  Andrew Smith replied 3 years ago.
Shut off the cold mains to the tank and empty the hot water completely, shut the hot tap again, then leave overnight. Turn on the tap in the morning and see if there is any water - if there is it will be coming from the heating. Just to make sure, you could turn off the supply to the heating tank and see if the water level drops.
Customer: replied 3 years ago.
Will do - thanks
Geoff
Expert:  Andrew Smith replied 3 years ago.
OK let me know
Customer: replied 3 years ago.
I left it until this afternoon and all I got out of the hot tap was about 1/2 a cup of water.There appears to be no appreciable difference in the level in the expansion tank. I assume therefore I have a leak but it is quite small. Can I also assume that this leak will be enhanced when the system is heated and under pressure.
Geoff
Expert:  Andrew Smith replied 3 years ago.
Yes, when the systems are heated they expand and exert more pressure. This expansion is taken up in the expansion tank, if the head of water above (2m) is more than it would take to leak into the other system then this is the way it will go. The two water levels will balance each other out and if it happens that the overflow id lower than that level, then this is where it will go. I suggest you change your cylinder and stop drinking or rinsing with the hot water until this is done - there may be residue of central heating inhibitor getting into the hot water system.
Customer: replied 3 years ago.
Many thanks
Geoff
Expert:  Andrew Smith replied 3 years ago.
Glad to help

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