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I have been trying to drain the cold water tank in my loft so I can re-support it underneath. I tied the ball valve back so that no water could get in and turned on the bathroom taps, but the tank doesn't seem to getting any emptier. Am I missing something here, or do the bath and basin tanks not take their water from the cold water tank?

Interesting. I assume the tank is not the one that tops up the central heating. I also assume you have a traditional hot water cylinder and not a combi boiler.
The cold water tank should therefore top up at least the hot water cylinder and possibly the bathroom cold water and the toilet as well.
For the job you want to do you could always bale the tank out by hand. But of course that would not solve the mystery.
Could you explain what you mean by the bath and basin tanks.

Yes, its the big plastic tank that holds the cold water. There is a smaller tank also in the loft. The boiler is an old style gas one in the kitchen and an immersion cylinder upstairs.

As I say, I assumed that by tying up the ball-cock valve and turning on the cold water taps ( sorry, did I say tanks instead of taps previously) on the bath and wash basin that it would empty the tank.

Is it possible that it would need to drain the immersion tank first?

Hi Gramski,

Try tying up the ballcock again and opening all the [b]hot[/b] taps in the house. It may be that the cold taps are all fed directly from mains water - mine are. Turning the hot taps on should drain down the big header tank via the hot water cylinder (which will stay almost full by the way).

hi
you would be better turning off your water at the mains and then turning on all of your taps in the house your cold should be running from the mains and hot taps abdviously feed from the header if when you turn on your hot tap and there is no water filling the level in the tank does not drop the only reason for this would be that the tanks are switched around try it with the other as i have seen header tanks have been mixed up so to recap if the level does not drop when you have the water off its the wrong header tank
i hope this helps

thanks Ryan