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How To – Draining a radiator quickly and without making a mess

As with many plumbing jobs, draining off a radiator has the potential to be a messy business. The scope for something to go wrong is big, but there are methods you can use to cut down the risk of any mishaps. In fact, if you follow these steps, then it’s possible to drain your radiator or, in fact, your whole central heating system, without any, mess at all.

Cat on Radiator


Firstly, we look at draining off an individual radiator using a draining kit:

1. Switch the boiler off and give the system time to cool down

2. Close the hand-wheel valve. If a thermostatic valve is fitted, unscrew the head and fit a dust cap.

3. Close the lockshield valve by turning it clockwise. If you make a note of how far you need to close the valve to turn it, then you should be able to reverse this later on to make sure it is correctly open. To ensure that the valve is completely closed, check with an adjustable spanner or pliers, but be careful not to tighten too much.

4. Use your kit’s diverting collar placed around the pipe and the catch tray beneath. It doesn’t hurt to have the catch tray on a towel, or something similarly absorbent. Sealing gel can also be used at the point where the diverting collar meets the pipe.

5. Loosen the cap nut between the valve and the radiator with a suitable spanner. If you hold the valve with a pipe wrench, this avoids slippage with the spanner and possible damage to the valve or piping. Once it’s loosened, use your fingers to continue opening the cap nut, while making sure you do not fully remove it. Water will now flow along the diverting collar and into the catch tray.

6. Using a screwdriver, open the bleed screw, allowing air into the radiator and increasing the flow of water from the valve at the other side.

7. If the catch tray fills up, closing the nut with your fingers should be sufficient to stop the flow while you empty out the tray.

8. Repeat this process until the radiator is empty.


If you are looking to drain a whole central heating system and can find a radiator with a drain off valve, then follow these steps:

1. Again, make sure your boiler is switched off and the system has cooled.

2. Find a radiator on the ground floor with a drain off valve.

3. You will also need a length of hose the right size to fit snuggly around the drain off valve. The hose should be long enough to reach outside of the property.

4. Fit the hose to the pipe. You may feel confident that you have a tight fit around the valve, but it is probably advisable to use a jubilee clip to ensure a tight seal and that the pipe will not move once the pressure of the water moving through it is applied. Just in case, it might be wise to have something absorbent like a towel beneath the valve.

5. Run the hose pipe outside, ideally to somewhere where the water will be able to run easily away – though not over flowers or vegetation. Remember, if crossing public areas, to take all necessary precautions for public safety.

6. Open the valves on all the other radiators, before opening the drain off valve. It will start to drain out, but can be made to drain much quicker by going to all the upstairs radiators and opening their bleed screws, forcing air into the system. After maybe 10 minutes, you should be able to open the downstairs valves without water coming out, and this further forces the water from the system.

7. Depending upon the size of the system, it should take about 15-20 minutes to drain completely.


Image credits: Kim -

Contact Plantool for expert advice on freephone 0800 334 5365

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