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How to replace a radiator

Difficulty rating: Medium

These jobs are only for a competent DIYer, so only go ahead if you're confident about your plumbing skills. Otherwise call a qualified plumber. Replacing a radiator should only take a few hours.

Before you get started on any of our 'how to' guides, please take a moment to read through our DIY safety tips.

1. Turning off the water supply

  • Your first step is to turn off the central heating and allow the water in the system to cool. Next you sort out the valves at either end of the radiator or towel rail:
  • At one end is the manual control valve that turns the heat on and off (fig. 1).
  • Turn this control to the off position by rotating it clockwise. If you have a thermostatic valve, make sure it's turned to 'off' and not just to the frost setting.
  • At the opposite end of the radiator or towel rail is a valve that controls the flow through the system. This is the lockshield valve (fig. 1).
  • Take off the protective cap. Turn the square top piece clockwise as far as possible with an adjustable wrench (fig. 2).
  • Count the number of turns needed, as the valve should be opened by the same amount when you replace the radiator.
 
The key parts of a typical household radiator.
Figure 1
Use a wrench to turn the lockshield valve clockwise to stop water flow through the system.
Figure 2

2. Draining the old radiator

  • Place a bowl or bucket under the manual control valve.
  • Grip the body of the valve with one adjustable wrench. Hold it steady while you use another wrench to gently loosen the nut that connects this bleed valve to the adaptor piece screwed into the radiator (fig. 3).
  • Now you need to vent the radiator of air to break the vacuum inside and allow the water to flow out of the control valve. Do this by opening the bleed valve at the top with a radiator key (fig. 4).
  • Hold a towel under the bleed valve to catch any drips.
  • Keep draining the water out of the control valve end of the radiator until the flow stops.

 

Helpful hint...

Plumbing involving pipework is covered by a number of safety regulations. If you're unsure about them, talk to a professional plumber.

 
Draining the radiator.
Figure 3

3. Removing the old radiator

  • Once the radiator is drained, loosen and undo the nut that connects the lockshield valve to the adaptor in the radiator.
  • You may have to gently push the central heating pipes and valves outwards to free the connections. But be careful not to bend them (fig. 5)!
  • Lift the radiator upwards to remove it from the wall brackets. You'll probably need help for this (fig. 6).
  • Close the bleed valve with the radiator key (fig. 4).
  • There'll usually be some water left in the bottom of your radiator or towel rail, so tilt it to one side and drain this into a bucket.
  • The water may be dirty, so place the radiator on old towels or sheets.
 
Vent the radiator with a radiator key to break the vacuum and let the water flow out.
Figure 4
To lift the radiator you may need to push the pipes outwards. Do this gently and without bending them.
Figure 5

4. Decorating behind a radiator

  • If you've removed the radiator to decorate behind it, you could unscrew the metal wall brackets to make repainting and wallpapering easier.
  • Note the brackets' exact positions so you can put them back using the same screw holes.
 
Lift the radiator upwards to remove it from the wall brackets.
Figure 6

5. Rehanging or hanging your radiator

  • When you're ready to hang or rehang the radiator, wrap a piece of PTFE tape (also known as plumbers or thread seal tape), about 150mm long, around the adaptor screw threads. Work in a clockwise direction (fig. 7).
  • Fitting a new radiator or towel rail that's the same width as your old one? Then fit the control and lockshield valves before installing the unit onto the wall. Next, open the valves to fill the radiator. By the way, make sure you follow the manufacturer's instructions.
  • Lift the radiator onto its wall brackets and tighten up the nuts that connect the valves to the radiator on both ends. You may need help to lift and hold the radiator.
  • Never overtighten compression fittings. Use just enough force to make a watertight joint - this is usually hand-tight and then a three-quarter turn with an adjustable wrench.
  • Open the manual control or thermostatic valve fully (fig. 1). Then open the bleed valve at the top (fig. 4). Water will now fill the radiator.
  • When the water has stopped gurgling, open the lockshield valve (fig. 1) by the same number of turns as you needed to close it.
  • Check all the joints are dry and tighten if necessary.
  • Turn on your central heating and recheck.
 
Wrap a piece of PTFE tape about 150mm long clockwise around the adaptor screw threads.
Figure 7

6. Painting new radiators

  • Apply one coat of primer (follow manufacturer's instructions). When it's dry, paint in your chosen colour, starting at the top and using vertical brush strokes.
  • Radiator paint is specially designed for metal and to resist high temperatures without discolouring. Most radiator paints are water-based.
  • Paint when the radiator is cold and allow it to harden. When you've finished painting, turn the radiator on within 24 hours, to make sure the paint 'cures' properly.
  • Don't paint over any valves or fittings - they could be difficult to operate afterwards.

 

Helpful hint...

After removing your radiator it's a good idea to bleed all the radiators in your system as air can move through the pipework.

 

7. Replacing a radiator with a larger or smaller one

  • If you're replacing your old radiator or a towel rail with one that's a different size, the pipework might not connect up exactly.
  • In this case you'll need to drain your central heating system so the pipes directly under the floor can be replaced or adjusted to fit onto the new unit.
  • If you don't have any experience with this kind of job, call in a professional. 
 

8. Bleeding your radiators

  • To make your radiators work better you need to bleed them every now and then. That's because over time, air builds up and creates a bubble inside the pipes, blocking the flow of hot water to the radiator.
  • First, turn up the thermostat on your heating system. Then touch near the top of all your radiators to see which ones aren't coming up to full heat.
  • Allow these radiators to cool. Then gently open the bleed valve at the top of each radiator with a radiator key (figs. 1 and 4).
  • You'll hear air escaping but close the bleed valve again as soon as water begins to appear.
  • Have a towel handy to catch any drips.
  • Don't bleed radiators when they're hot as you'll get scolding steam coming out of the bleed valve.
 

9. Stopping your radiators corroding

  • When air and water meet in a radiator they cause corrosion and this reduces the efficiency and lifespan of your radiators.
  • Deal with this by adding anti-corrosion fluid to the system (as usual, carefully read the manufacturer's instructions).
  • With an open vent system (one with an expansion tank or cistern), put anti-corrosion fluid into the cistern.
  • For sealed systems, you can buy a cartridge of inhibitor that's injected through the radiator's air bleed valve.
 

Tools for the job


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