Draining hot water - vented cylinder systems
Before working on the hot water pipes, switch off the boiler and immersion heater.
Close the cold supply from the storage cistern in the attic to the hot water cylinder. It seems odd to do this, but it is really quite logical. The cold supply to the cylinder is what forces the hot water out of it when you open the taps. So by turning off the driving force, you also turn off the hot water.
If there isn’t a valve for the cold supply or you can’t identify it, follow the instructions earlier for emptying the cold water cistern in the attic and open the cold taps. The effect will then be the same, as no water is available to drive the hot water from the cylinder.
Emptying the WC cistern
This can be done using the same process as for the cistern in the attic. Remove the lid of the cistern and tie up the ball valve using a length of wood across the top.
Some WCs have an isolating valve in the pipework just before the cistern, which can be closed instead.
Once the supply has been stopped, the water in the cistern itself can be removed by flushing the WC.
Emptying the cold storage cistern
Switch off the rising main or tie up the ball valve.
Open the taps supplied by this cistern to remove the water.
This will empty the tank down to the level of the outlet pipe.
If the latter is not an option (the taps can’t be opened for some reason) or to remove the water below the outlet level, use a bucket to empty it, or drain it out by syphoning with a length of hosepipe routed from the bottom of the cistern to the nearest bath.
Emptying the hot water cylinder - vented type
Turn off the boiler and immersion heater and close the cold feed as described earlier.
Switch off the power supply to the immersion.
Open the hot taps to release water.
At the base of the cylinder there will be a drain cock. Attach a length of hose to this with the aid of a jubilee clip if necessary. Run the hosepipe to an outside drain or sink/bath/WC at a lower level.
Open the drain cock and the water will be released from the cylinder.
On some systems, there is also a coiled pipe full of water within the cylinder. To drain this, switch off the electrical supply for the heating system, and close the supply of water to the expansion tank. This is a small cistern located in the attic (usually) which supplies additional water to the heating system when required. It also allows excess water caused by expansion to be released.
Drain the water from this coiled pipe using the cock located for this on the boiler.
If you are not able to identify this for certain, you should consult a professional plumber.