A-Z of DIY & Building Guides How To Drain A Plumbing System

Date Published:

18/05/2009

Step Two

Look for the drain nozzle on your system. This is a brass extension that can be fitted into a hosepipe to drain the water out of the system. It will normally be fitted in the lowest part of the system and there may be more than one drain nozzle. You may need to use both to take all the water out of the pipes.

Fit a hosepipe to the nozzle and run the other end to a point outside where water can drain away safely. Open this valve by turning the square brass drain cock on the end of the nozzle. Use an adjustable wrench.

Step Three

Open the bleed valves of the upstairs radiators with a radiator key. Then move to the downstairs radiators and do the same.

Sometimes an air lock will stop all the water draining out. To check, undo the ball valve arm and allow around 150mm of water to fill the expansion tank. Tie the valve up again. This water should drain out through the hose almost immediately. If it doesn’t, connect the open end of the hosepipe to your cold water pipe and open up for a few seconds to force a jet of water back into the system, breaking the air lock. Repeat if necessary until the water in the tank drains away completely.

Step Four

Once you’ve carried out the work, disconnect the hose and close the drain cock. Close all the bleed valves on the radiators. Untie the ball valve so that the system refills.

When the tank stops filling, bleed all the downstairs radiators, followed by all those upstairs. Turn on the gas or electricity and turn on your boiler. Run the system and check for leaks. You may also need to re-bleed the radiators as air is forced around the system.