Water header tank has broken ballcock. Not working properly. I have turned off the tap supplying the header tank - what are the consequences of doing that and can we continue to use water "normally" while that header tank is not supplied any water??
The header tank is there to provide water pressure to your hot water system. You'll still get cold water just fine* but if you use more hot water than the volume of water in your header tank you'll start to empty the hot water cylinder and could end up burning out the element if you drain it too far. What do you mean by the ballcock being broken? If it's water continuing to flow into the tank when the ballcock has risen as high as it'll go, that's simply a washer that needs replacing. Easy job.
Edit: trying to make more sense
Edit 2: * Actually this depends on how the house is plumbed. Turning off the supply to the header tank off may also (eventually) cut off water to bathroom and cistern.
YouTube will be your friend here - "replace header tank ballcock washer"
Is the overrunning water the problem?
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My place used to have a header tank but the previous owner took it out and installed a re-circulation pump to suck out the hot water from the tank. You need to create enough negative pressure but was a decent stop gap measure without replacing with a high pressure system.