How to drain the cold water tank

Need to drain the cold water tank? It’s not a difficult task, and in most cases you shouldn’t need to go into the loft. Simply do the following:

  1. Turn off the mains stopcock, either on the rising main or outside the property.
  2. Turn on the hot taps.

And that’s it – when they stop running, the tank should be empty. Well, not quite in fact – there will still be a small amount of residual water below the outlet points. If you need the tank to be completely empty, then this water will have to be bailed out, or removed with a wet vac.

If you can’t find the stopcock, or for some reason it is inaccessible, you will need to go into the loft and close the isolation valve on the supply to the ballcock with a screwdriver. If there isn’t an isolation valve, you can lay a piece of wood across the tank and tie the ballcock up with a length of string or garden twine.

An empty tank is a splendid opportunity to remove any limescale or sediment which may have gathered in the bottom – or dead rodents and insects. Buy a lid to prevent any animals or loft debris from getting in the tank – you should be able to get one that suits its shape and capacity. Ideally, you should fit a Byelaw 30 kit (or Byelaw 60 kit if you live in Scotland). These kits consist of a number of components which protect the water from external contamination.

Draining the cold water tank will also stop the flow of hot water in your house, as it is gravity acting on the water in the loft which effectively pushes hot water out of the top of the hot water cylinder. Consequently, this means that draining the cold tank will not empty the hot water cylinder – the hot water in the cylinder will simply be replaced with cold water from the cold water tank until the tank is empty. If you want to drain the hot water cylinder, you will need to shut off the supply from the cold water tank and attach a hosepipe to the draincock on the supply pipe to the cylinder.

If you have an indirect plumbing system, i.e., your bathroom taps are supplied via the cold water tank, then you should open the cold taps in the bathroom until the tank is empty. This will save you from having to waste all of the hot water in the hot water cylinder.

Refilling the tank is easy: simply ensure that all taps and drain-off points are closed. Untie the ball valve, or open the isolation valve or stopcock. If you have carried out any maintenance on the cistern while it was empty, then you should check it for leaks while it is filling.

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