How to Drain a Radiator Without Draining the System

Last updated on October 13th, 2024

Emptying a single radiator is sometimes useful for adding chemicals, replacing the radiator, or connecting a hose to the radiator valve to drain the system when there’s no drain-off valve.

I have been a full-time heating engineer for well over a decade and have drained many radiators and heating systems along the way.

Video Guide

Step-by-Step Guide

To drain a single radiator, you will need to isolate it from the system by closing the two radiator valves.

The easiest way to drain a radiator is to leave it in place and empty the water from it into a tub, but doing it this way can take a long time. You can use any tub to do this but a Plumb Tub is by far the best thing to use. They clip around the pipe and catch the water if it runs down the pipe.

Here’s how:

1. Put a towel down

Put at least one old towel down under the radiator valves and around the pipes to catch any water spills. The water could be black and sludgy and won’t come off anything it touches so make sure your carpet and flooring is well covered.

2. Close the valves

Close both radiator valves fully by turning them clockwise as far as they will go. Turn thermostatic valves to 0 or off, and lockshield valves will need an adjustable spanner or water pump pliers to turn them.

3. Place a tub under a valve

Place a tub under a radiator valve to catch the water emptying out. If you don’t use a Plumb Tub it will be a lot harder to catch the water and much more likely to make a mess.

4. Open the bleed screw

Hold a bucket or towel under the bleed valve and open the bleed screw with a key to release the pressure. Catch the water that comes out. Wait until the water stops coming out, if it doesn’t stop, there must be a faulty radiator valve that’s not working so you’ll have to drain another radiator or drain the system.

5. Crack a valve nut

You might need to hold the valve still with some water pump pliers but most of the time you don’t. Crack the side nut on the valve connecting the valve to the radiator by turning it anti-clockwise with an adjustable spanner. Make sure the bleed screw is still open and wait for the water to come out of the valve nut.

6. Let the water fill the tub

Catch the water from the valve nut in the tub and wait for it to fill up and then tighten the nut to stop the water coming out.

7. Empty the tub

When the tub is filled with water, empty it into a bucket to save you from having to keep walking away, but you can take it to a toilet or drain outside to empty it. Repeat the process until the radiator is empty. This can take a long time so emptying the tub into a large bucket will save some time.

Summary

Emptying a radiator can be a nightmare sometimes, especially if it’s huge. If you have ancient radiators and valves, or you know the system water is really dirty, you might be better off draining the full system.

However, draining a new small radiator is quite easy most of the time, and a Plumb Tub will make the process much better.

Feel free to ask any questions in the comments below, and I’ll do my best to help. If you found this post helpful, please consider sharing it.