How To Drain A Plumbing System
An adjustable wrench
Timber batten and string
Hosepipe
Radiator key
Budget
Radiator keys cost around £2 from any DIY store
Time
One to two hours
Skill
Intermediate
Step One: Stop The System From Refilling
Turn off the gas or electricity supply to the boiler. Go into your loft and find the expansion tank for the system. This will have a ball valve that controls the flow of water from the mains into the system. Lift up the ball valve arm and tie it to a timber batten placed across the tank. This will stop the system re-filling.
Step 2: Drain The System
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 3: Bleed All The Radiators
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 4: Reconnect The System
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.
- Newer systems, like combi boiler systems for example, are known as sealed systems and rely on mains water pressure. In these cases, call in a qualified heating engineer to carry out the work.
- If you have very old radiators, consider asking a qualified heating engineer to flush the system. Find one on the Gas Safe Register.
- Cleaning out the sludge will increase the efficiency of the boiler.
Illustrations: Ed Roberts
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