DIY How To

How to Fit, Bleed Radiators

DIY Projects - Radiators

Radiators come in a range of sizes and designs. The larger the radiator the more heat it gives out, to increase the heat output even further, radiators can come with fins on the back to increase the convected area or even have two radiators back to back which creates a double radiator.

Most of the heat given off by radiators is actually convected heat, as the air touching the radiator warms up it rises towards the ceiling, cool air then replaces this warm air, which is also heated by convection and rises upwards, this process continues slowly warming the room until the radiator is switched off by a roomstat or TRV.

Radiator and valves

A radiator will have a handwheel valve or thermostatic radiator valve (TRV) which is used to control the flow and thus the temperature of the radiator.

The lockshield valve is used to balance the system and is not normally adjusted.

The bleed valve is used to release any trapped air that has built up in the radiator. Trapped air prevents the radiator from heating up properly.

DIY Projects - Fitting radiators

A radiator can be fitted on any wall, a popular place to fit radiators is under a window, this used to be ideal because any draughts from the window encouraged the air to circulate. Nowadays this has little effect due to many homes having double glazed windows but it is still a popular position because usually the wall space below a window is not used for anything else. Air needs to circulate freely around the radiator, so if you have long curtains it would be more efficient to place the radiator on another wall. Try to avoid placing furniture in front of radiators, due to the radiated heat being absorbed by the furniture.

Mark out wall

  1. Mark the centre of the window or the centre position of where the radiator is going to be.
  2. Measure the distance between the centre of the radiator fixing lugs and divide by 2
  3. Mark two more vertical lines this distance either side of the centre line.
  4. Hang a fixing bracket onto the fixing lug and measure from the floor to the top of the bracket. Add 150mm floor clearance to this measurement and mark a horizontal line through the bracket vertical line.
  5. Hold the bracket with its top inline with the horizontal line and the bracket holes in line with the vertical lines and mark the drilling position.
  6. Drill and plug the holes and screw the brackets in place.

Top TipThermostatic radiator valves can sometimes be directional. Use the arrow marked on the valve to ensure it is fitted correctly.

Hang the radiator on the brackets and connect the valves to the bottom of the radiator. Line the feed and return pipes up with the bottom of the valves and connect up.

DIY Projects - Bleeding radiators

If a radiator feels cool at the top and warm at the bottom it will probably have air trapped in it which must be removed. To remove any air trapped in a radiator you need to 'bleed' the radiator. All radiators have a bleed valve on one of the top corners.

Switch off the boiler and wait for the circulating pump to stop, place a jar or rag under the bleed valve and using a special bleed key or in some cases a flat screwdriver, turn the valve anti-clockwise approx 1/2 turn. You should hear a hissing sound as the air releases.

Safety AdviceBe careful when bleeding a radiator, the water can be very hot. Keep children and animals away.


If you place your hand on the top section of the radiator you will feel the heat rising.

Keep the key on the valve so it can be closed as soon as water starts to come out.

Don't remove the valve completely or you won't be able to stop the water coming out.

Bleed key

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