DIY How To

Draining a Radiator

This project is sponsored by Draineasy

A radiator may need draining for various reasons, it may be corroded and needs to be replaced, It might be being replaced by a different size radiator or it could be that you need to replace one of the valves. With a bit of care, individual radiators can be drained without draining down the whole system.

Draining a radiator

Thermostatic rad valve Close the handwheel valve or where a thermostatic valve is fitted (as shown) unscrew the head of the valve using the knurled nut (should be hand tight only) and fit a dust cap.
dustcap The reason to fit a dust cap is you cannot normally fully close a thermostatic valve. If you don't have a dust cap one can be purchased from a home improvement store.
lockshield Close the lockshield valve by turning the valve clockwise, some lockshield valve caps are dummies and do not actually turn the valve. Make a note of the number of turns required to close it, so that it can be re-opened by the same amount.
It is important to re-open it the correct amount of turns because this is the valve that balances the radiator within the system.
lockshield valve To make sure the lockshield valve is completely closed remove the cap and use an adjustable spanner to check it is completely closed.
Make sure the carpet or floor is well protected against spills by covering around the pipes with newspaper or an old towel.
lockshield valve Place the spanner on the shank of the valve and turn it clockwise, do not overtighten.

To check both valves are fully shut off open the radiator bleed valve and only a small amount of water should be released. If a steady flow of water is released check the valves are shut and try again. If the water still comes from the bleed valve the whole system will need to be drained.
drain radiator Fit a draineasy kit or similar to collect the water. To prevent damage to the pipe while unscrewing the cap-nut from the valve, hold the valve with a pipe wrench. Loosen the cap-nut which attaches the valve to the radiator with a suitable spanner.
drain radiator Slowly open the cap-nut until the water starts to slowly drain out. The water will drain into the catch tray. If the water slows you can open the radiator bleed valve to allow air into the radiator, this will increase the flow of water.
drain radiator When the catch tray starts to fill close the bleed valve whilst you transfer the water to a bucket and repeat the process until all the water is drained off.
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