Draining a Domestic Plumbing System

draining a plumbing system

If you are planning to leave your house for any length of time, it can be a good idea to completely drain your plumbing system to avoid frozen and burst pipes (especially in houses with older systems). There are also other times when you might need to drain the system and the process is fairly simple.

Draining the Full System

1. Switch off the boiler or immersion heaters, and rake out any solid fuel boilers (allowing it to cool).

2. Turn off the main stopcock in the rising main, and run off all the water from hot and cold taps.

3. If there is a draincock on the rising main, drain the water left in the pipe using that.

4. Flush the toilets.

5. Drain the hot water cylinder.

6. You don’t really need to drain the central heating system, but make sure it contains a suitable antifreeze.

7. It is a good idea to place a note on the boiler or immersion heater to tell you to fill the system before lighting the boiler or switching on the immersion.

Refilling the system

To refill a drained system, close all the taps and draincocks, then open the main stopcock. Keep an eye on the float valves as the system refills to make sure they are working correctly. If you find that your taps are spluttering after the system is refilled, you will need to flush it out with mains pressure. To do this, attach a hose to the tap, and the other end to any tap on the main. Now open both taps and allow the mains pressure to flush out any air pockets.

In an Emergency

In case of emergency, i.e. a leaking pipe or WC, you might need to drain specific parts of the water system.

Draining Cold Water Pipes

– Turn off the main stopcock on the rising main. This will cut off the water to the kitchen taps and all other taps in a direct system.

– Open the taps until all water has drained out.

– In the bathroom, close the valve on the cold feed pipe from the cistern and open all the cold taps in the bathroom. If you can’t find the valve on the cold water cistern, you can tie up the float arm so that it does not refill automatically.

Draining Hot Water Taps

– Turn off the immersion heaters and boilers

– Turn off the valve on the cold feed pipe to the hot water cylinder. Now run the hot taps until the water stops flowing. At this point the cylinder will still be full.

– If there is no stop valve on the cold feed pipe, tie up the float arm on the storage cistern in the loft, run the cold taps to empty the cistern and then run the hot taps. If you run the hot taps first the cold water from the cistern will flush out all of your hot water in the cylinder.

Draining a WC Cistern

– Tie up the float arm of the WC cistern.

– Flush the WC to empty it.

– If you want to empty the pipe supplying the WC cistern, either turn off the main stopcock (in a direct system) or close the valve on the cold feed pipe from the cold water storage cistern and then follow the steps above to empty the pipes.

Draining the Storage Cistern

– Close the main stopcock on the rising main and open all the cold taps in the bathroom (or hot taps if it is a direct system) until they stop running.

– The water left at the bottom of the storage cistern will need to be bailed out by hand using a jug or other container.