Expansion Tank

surfrider · 30 Dec 2008

I have an open vented system and recently noticed that water was coming out of the overflow from the expansion tank in the loft. Having checked the tank, the water level was above the ball cock and so thinking the ball valve was the problem, I replaced it. However, the problem is still there, although it is not apparent where the water is coming from. The water is fairly clean and cold.
Having read other posts, is would seem that this may be related to the heating coil in the hot water tank.
I would be grateful for any advise on this and if there anything I can do to establish whats causing this problem ?

Agile · 30 Dec 2008

Whatever it it its imperative that its dealt with otherwise your system will be sludged up in a few days and will need power flushing.

It sounds more likely to be a problem with the heating system, reducing the poump speed might reduce the problem for the moment but you must get it dealt with quickly.

Tony

namsag · 30 Dec 2008

Dont talk sh#te it will not sludge up in a few days. You after a job with BG.

It needs fixing though as you will be bathing in water that is mixing with what is going through your rads .
In time it will have an adverse affect on radiators etc as the fresh oxygenated water will cause corrosion

surfrider · 30 Dec 2008

Many thanks for your advice.

The reason I thought it may be related to the hot water heating coil is that it's only recently happened. The pump speed has not been altered.

I don't think this is an over-pumping problem, so the water must be coming up the feed pipe from somewhere.

D_Hailsham · 30 Dec 2008

surfrider said:
I have an open vented system and recently noticed that water was coming out of the overflow from the expansion tank in the loft. Having checked the tank, the water level was above the ball cock and so thinking the ball valve was the problem, I replaced it.

Did you adjust the ball valve so that, when the water in the CH system is cold, the level is about an inch above the bottom outlet?

Is water coming out of the vent pipe - the one which hangs over the tank.

When the heating is turned on, the level in the tank should rise as the water expands - but not so it goes down the overflow.

surfrider · 30 Dec 2008

Yes the ball valve is adjusted correctly and there are no signs of water coming out of the vent pipe. I don't think this is related to expansion due to the amount of water that is coming into the tank. Whatever is causing the problem I think is due to something else in the system.

Is it possible for water to enter the heating coil and thus the heating system?

The head of water on the main water tank is at a higher level than that of the expansion tank.

Agile · 30 Dec 2008

I had interpreted what you had written as describing pumping over.

In that case its not so urgent if its only coming out of the warning pipe.

It could well be a leaking heating coil in the cylinder.

Since the flow is one way from coil to heating system your hot water should not be afected by the heating water.

However, its still bringing new oxygenated water into the heating circuit so its still important to sort it out within a very few weeks.

To be 100% sure of the cause tie up both ball balves, dont use any water and see if the situation continues and the level falls in the cold water cistern.

Tony

surfrider · 30 Dec 2008

Tony,

Many thanks for your advice, I will give it a try. But before I do, here is some further information.

The water is not coming in via the vent pipe or ball valve so it must be entering via the 15mm outlet from the tank. The rise in level is slow, it takes nearly all day and the water remains cold & clean.

If it is the heating coil, I assume this will mean replacing the hot water cylinder.

How big a job is this and what sort cost would be involved ?

namsag · 30 Dec 2008

To the OP expect to pay anywhere from £300 to £600 yes new cylinder req ,but depending on size and your existing pipework to it depends how long it will take some can be done without draining the heating which will also save time thus labour charges.

Agile get a grip the water does not move 1 way the water from the heating circuit will definetly be moving into the domestic hot water. Thus into bathing water and some people also fill the kettle from the hot tap etc etc

tincup · 30 Dec 2008

Hi

It could be a washing machine valve or shower mixer valve letting by. I have had one of each in the past year.

HTH

namsag · 30 Dec 2008

NO it cant

spudkey · 30 Dec 2008

have you got two tanks in loft if so is the f&e tank higher than the domestic cold water tank

D_Hailsham · 31 Dec 2008

namsag said:
Agile get a grip the water does not move 1 way the water from the heating circuit will definetly be moving into the domestic hot water. Thus into bathing water and some people also fill the kettle from the hot tap etc etc

I would have thought that, if water was leaking from the coil into the HW cylinder, the level in the F/E tank would go down as water is being lost from the heating system. But the ball will open to allow the water to fill up to the correct level. Any rise in level in the F/E would just be due to heat expansion.

Any increase in the F/E water level greater than that due to expansion must be due to either a blocked feed or water entering the system from somewhere else. If there was a blocked feed, the water expansion when heated would have to come up the vent pipe. But the OP says no water is coming out of the vent pipe - so a blocked feed can be discounted. So water must be entering the heating circuit from somewhere else.

namsag · 31 Dec 2008

Nope as water always finds its own level the water that was coming out of heating circuit would be getting replaced just as quick from the water from cylinder .
Because its a hole in coil it does not mean water would only be flowing out of it or into it , it would be a two way exchange .

D_Hailsham · 1 Jan 2009

namsag said:
Nope as water always finds its own level the water that was coming out of heating circuit would be getting replaced just as quick from the water from cylinder.
Because its a hole in coil it does not mean water would only be flowing out of it or into it , it would be a two way exchange .

What level will the water find? Presumably whichever water level is higher in the two tanks (F/E and cold water). If the cold water tank level is higher than the F/E tank level, then there would be a transfer of water from the cylinder to the F/E tank via the hole in the coil; and vice versa.

If the leak was from the CH system into the HW cylinder, then surely the water level in the cold water tank would rise and there would eventually be water coming out of the overflow - assuming no water was drawn off. The level in the F/E tank would not change as the loss would be made up by the ball valve opening.

The direction of exchange will be determined by the relative water levels.

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Expansion Tank

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