CH Expansion Tank Overflow

[AndrewB]

Before you all shout 'ballcocks' - it isn't, been there and done that! This is the CH expansion tank in the loft - started overflowing so I replaced the entire ball-valve (as you do) and bent the arm down and even emptied out the tank of a few gallons to lower the level. It is definitely not the cold feed but after a few days it fills up again and drip drip drip (it is driving me nuts!)

Either it is the hot vent or the hot feed from the boiler. At this present time the CH is off but the hot water is on timed (although this does not affect the problem), I have turned down the pump to its lowest setting (on the advice of a plumber) and yet its still drips intermittently and it is possibly worse when the boiler is running but I have not monitored this too precisely. The stat on the HW tank is set at around 50 deg - adjusting this also makes no difference.

Before I give in and call in the professionals - does anyone have any idea what the cause might be.

All suggestions welcome

Thanks

Andy

 

[breezer]

since the expansion tank is over filling what happens if you turn the supply to the ballcock off?

My thinking is that the water must be coming in from somewhere, and this would prove if it is the ball cock or not

 

[masona]

Could be the coil inside the hot water cylinder is fractured,the hot water & central heating could be crossing over to the hot water going back to the expansion tank.Turn off the water supply to the main storage tank (not the expansion tank) and see what happen.

 

[COG]

IF THIS IS A SUDEN PROBLEM IT COULD BE THE COIL INSIEDE YOUR CYLENDER IS LEAKING,PASSING WATER FROM THE PRIMARY .NOT EASY TO TEST,IF THE LEVAL OF WATER IN YOUR FEED TANK TO YOUK CYL IS HIGHER THAN YOUR EXPANSION TANK THIS IS ENOUGH HEAD TO GET IT THROUGH THE LEAK IN COIL. "HARD TO EXPLAIN". IT COULD ALLSO BE TOO MUCH EXPANSION, FROM MUCKY SYSTEM WATER OR TOO MUCH INHIBITOR .THE MOOR DEBRI IN THE WATER THE LOWER THE BOILKING POINT AND MORE EXPANSION . COG[/i]

 

[Jim]

had exactly this problem and found that the cause was the coil in the hot water cylinder was fractured. I replaced the cylinder and this solved the problem.

 

[masona]

Jim,

Out of interest, did you see where the fractured was ? on the joint or was the coil split ? or couldn't see.

 

[Jim]

I didnt actually inspect the coil myself. However I know that the coil itself had deteriorated to the point where there was a crossover between the central heating and the water heating functions. This was caused by the coil having corroded enough to leak out in the hot water cylinder. It manifested itself by constant overflow of the expansion tank and when I examined this tank the water in it was in fact hot when the central heating system was on. It would in fact get a surge of hot water and even come over the side of the tank and thro ceiling sometimes.
Jim

 

[masona]

It's a pity the coil not made of stainless steel or plastic instead of copper,maybe cost ?

 

[AndrewB]

After a bit more research I too have stumbled across the hot cylinder coil issue and the crossover - I have isolated the supply to the cold feed and the tank still fills. I seem to recall a couple of my neighbours both having new cylinders in the last year or so (sadly both since moved on so I can't ask them) so it looks as though it is my turn.

The advice offered here seems to confirm my worst fears - now where did I put that plumber's phone number!!

Cheers for the info - much appreciated

Andy

 

[Gees]

Just a quick reply to masona... the coil is a heat exchanger and thus must be made of the best possible conductor of heat... Copper.

 

[TopDog129]

As a temporary measure to this problem would there be any issue in putting a one way valve between CH overflow tank and the boiler thus the water is never allowed to reach the CH expansion tank!

Longterm what danger is there of leaving the valve in knowing that the coil has a leak!

 

[Gees]

Would that not cause a build up of pressure and consequent leaks?