Overflowing CH expansion tank

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There is a small expansion tank for the CH and HW system in the loft. It fills to overflow ever so slightly. I have emptied the tank and replaced the ballcock and valve, which doesn't seem to leak/drip, but within a day the overflow pipe is dripping again and the expansion tank has filled above the ballcock again. There is no water in the ball of the ballcock, which seems to be working perfectly, but the water must be getting in somehow when the HW/CH system is on and hot water flows into the expansion tank. Mystified!
 
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it may be the ball cock valve is dripping, empty out some water and see
 
there is a good chance you have a hole in the coil of your hot water cylinder. Double check the ball valve first.
You say hot water flows into the tank what do you mean by this? is the tank getting hot or is hot water flowing from somewhere.


Brian
 
taydo said:
there is a good chance you have a hole in the coil of your hot water cylinder. Double check the ball valve first.
You say hot water flows into the tank what do you mean by this? is the tank getting hot or is hot water flowing from somewhere.


Brian

Thanks Brian,

I have found that hot water is flowing out of the vent pipe into the expansion tank, as soon as the pump starts, and then flows back into the system through the return from the expansion tank. I think the pump was originally positioned incorrectly, after the boiler and before the vent pipe (in flow terms) rather than after the vent pipe. I'll have to get that fixed too. (It may also explain why I have had to replace 4 radiators in the last 3 years.

But that wouldn't explain where the extra water is coming from. I have checked the ballcock and valve and there is definitely no leak or dripping.

If there was a leak in the coil of the hot water cylinder then water would be forced by the header tank (which is higher than the expansion tank) into the system and up into the bottom of the expansion tank????????

How can this be tested?

Nigel
 
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I don't understand
b1lb0b4gg1ns said:
"If there was a leak in the coil of the hot water cylinder then water would be forced by the header tank (which is higher than the expansion tank) into the system and up into the bottom of the expansion tank????????


If by header tank you mean the big cold water tank - which feeds the huose taps, then yes. Small one is the heating header tank. If you are getting new water into your heating all the time then yes that will rust your rads. The "Pumping-over" is a separate issue, though it contributes to rusting too.

Yes the vent pipe (which goes over the top of the heating header tank) must be connected "clean" to the boiler - no pump or valves in the way. The feed & expansion pipe should be next, then the pump.

There's hardly a need to test that the coil is perforated. As you say there's nowhere else the water can be coming from. You could turn off the supply to the heating tank if you're still doubtful!
 
Thanks Chris R in Antarctica. I may try that, but I've just thought that if everything is switched off, then if water is 'leaking' into the coil, then the ballcock valve in the main Header tank should be dripping. So I'll try that first.

Thanks for all the help guys - I was going nuts!

Nigel
 
It's such a big tank you'll find it drips all day. You could turn off IT'S supply andwatch for a level drop - after several hours. I "see" coil- leaks when I change boilers - the primaries don't quite go dry.
 
The ballcock valve in the main header tank is dripping even with every tap, washing machine etc switched off or isolated.

In the return copper pipe from the expansion tank I found a tiny pin hole which was leaking (fixed now), so I can believe that the coil in the hot water cylinder may have corroded somehow.

I've checked the radiators and there are cool to luke warm at best at the bottom (hot at the top). The system must be well sludged up. I can't see any alternative but to replace the hot water cylinder and coil, and drain and flush the entire system and every radiator, topping up with a rust inhibitor. I'm just deciding whether to do it myself or get a plumber in.

Thanks for all the help. Are you really in Antarctica?

Nigel
 

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