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Help - cold water tank in loft water level decreases when no water is used

2 floor Victorian house with a cold water tank in the loft. no 2nd floor bathroom, bathroom moved to down stair extension (is like this when we got the property).

Recently, been told our meter is constantly running and suspect possible leaks. One of them could relating to this cold water tank, been told to check ballcock valve etc, all looks fine, water stops when you lift the ball valve upward. No water drips or wet patches anywhere.

Until I was curious and hold the ball valve upward for 10 mins, to be concern the water level of the cold water tank decreases....!! help!!!
What does this implies? internally leaking to where???

2 Answers from MyBuilder Plumbers

under ground floor,have you checked your toilet it may have internal overflow allowing water to flow into toilet bowl.


Answered 27th Aug 2018

Yes, as D&R said the WC is a good thing to check, however you could have an underfloor leak.
Another thing to check if you have a gravity fed heating system is there is no overflow from the small header tank if it's at a lower level than the main tank. What you are looking for if this is the case is perforation of the HW cylinder heat exchanger. If it is overflowing from the small tank then tie up the ballvalves or close the service valve to the main tank & leave it till the water level stops dropping. The level in the main tank should now be the same as the surface level in the small tank, = perforated heat exchanger. Whilst you conduct the latter test, also check your water meter. If it's still moving then you have a secondary problem too.


Answered 19th Sep 2018

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