Header tank constantly dripping but not overflowing

Hi all,

I am a complete novice when it comes to DIY so apologies if I use the wrong terminology. I have recently moved into an ex authority house (1970's mid terrace) and have had a few problems related to the plumbing. My main cold water tank and header tank are located in a cupboard on the same floor as my bedrooms and bathroom. The header tank is above the cold water tank and very difficult to get to due to it being too high to get to and messy plumbing. I can only see whats going on in there with a torch and a mirror. Anyway the water level in the tank seems to be well below the overflow pipe yet the inlet connected to the ball valve is constantly dripping, 24 hours a day. Every time I look, the water level is always about the same yet it's got to be draining somewhere as the water level isn't rising?

I initially thought there might be a leak from one of the radiators but there are no signs of dampness by any of them, downstairs the floor is concrete so the plumbing is all above the floor and all looks fine. There are no damp patches on the ceiling and everything else appears normal. Any ideas?

I'm not sure what you are describing. Usually the header tank that is filled with cold water from the mains is located about the hot water cylinder. I'm assuming this is what you are referring to.

A slow drip can take ages to raise the level in a header tank noticeably & and that's if no water is being used for several days.

Lift the ballcock up with your hand and hold it for a few seconds to see if the dripping stops. if it doesn't then you probably just need to re-washer it.

If it does stop, then try this. Allow the hot water cylinder to cool completely. then when you've finished using water for the day, pour some water into the header tank slowly just until the dripping stops and no more. Then before anyone uses any hot water in the morning see if the water level has fallen during the night due to a leak. If so, it will be dripping again. If it's not dripping you don't have a leak.

What may be happening is that the hot water cylinder cools as the hot water is used. Cool water occupies less volume than hot water and so the drip replaces the volume as it cools. This is why you must make the test with the cylinder cool.

Assume that by header tank you mean FE (feed and expansion tank) for the central heating circuit.

Could be that as the heating gets hot, there is some evaporation through the overflow pipe, which causes a drop in level of water. Easiest way to check if there is a leak somewhere would be to slightly overfill the tank until it drips no more and leave the heating off, and see if it begins to drip again after a while.

It might be a tiny loss of water somewhere which you don't notice since the heat of the pipework will dry it. Or it could be something else Check all way round the FE tank as well since it may be escaping from the outlet pipe at the base, and is soaking into the supporting timber and evaporating or soaking into something from there.

Some confusion and cross misunderstanding is going on there!

Just to confirm--
the OP is saying that the central heating feed and expansion tank is the one that has a dripping ball valve. (Not the cold water tank that feeds the hot water cylinder and domestic hot supply.)
The OP is correct in his thinking, ie that if it is dripping, but the water level is not rising and then eventually going through the overflow, then it must be going somewhere.
As this is not happenning and there is no evidence of a water leak, I would suggest that the drip is very slow, and that the water is merely dissapearing due to evaporation, either from the expansion tank surface, or mopre likely from a very slight weep at some joint on a hot pipe.
(If the drip is greater than this, I have no idea!)
The ball valve still needs sorting out--probably cleaning, new washer and ensuring it is seating OK when the arm rises.

Finally, is the OP certain that it is "always" dripping, and not just intermittently when any pressure surge occurs?

Sorry, Dexterous --you type and reply faster than me

No problem Tony - nice to see that we're pretty much in agreement.

Hi guys,

Thanks for all the responses, sorry for the confusion but yes I am referring to the F&E tank with the dripping ball valve. There could be a number of problems here and I believe one is that the ball valve needs a new washer, unfortunately it is nigh on impossible to get at due to it's position in the cupboard and the plumbing infront of it. I am however getting both tanks put into the roof over the next couple of months.

The dripping is definately constant but we think we may have discovered what may (hopefully) be the cause of the problem. The system was recently drained to install a new diverter valve and after listening to the system today as the hot water was switched on it sounds like lots of air is trapped in there. The radiators have been bled but we discovered the air release valve (sorry I don't know the technical name for this) had seized so no air could escape which in turn perhaps is causing a very slow filling, hence the constant dripping but not rising water level. Anyway we seemed to have freed this valve up now and you could hear air escaping (slowly but definately happening) so perhaps it's just a case of waiting for the system to sort itself out?

Sounds a possibility