How to work a room radiator

Updated February 21, 2017

Correctly balanced radiators are an excellent way to heat rooms. To work efficiently they must be adjusted so that each radiator produces enough warmth to do its job without depriving other radiators of the hot water supply. Making sure that a radiator gives out enough heat, without depriving the next radiator of all the hot water, necessitates adjusting three valves on the radiator. The procedure needs no previous plumbing experience.

Run the heating system to warm up the radiator. Feel both pipes entering the radiator and note which heats up first. This is the feed pipe and you will need to identify it later. When the radiator is warm, switch off the central heating pump and turn down the main thermostat to prevent the heating coming on. If you are setting more than one radiator, start at the highest point in the building, and work your way down.

Carefully touch the bottom of the radiator. If it is too hot, wait until you can comfortably touch it. Check the temperature across the entire height of the radiator. The temperature should be consistent. If the top part of the radiator feels cold, there is an air block in the radiator.

Locate the bleed valve, mounted at one end of the pipe forming the top of the radiator. It looks like a small square nipple. Use a radiator bleeding key to gently unscrew the valve whilst holding a container beneath it to catch any drips. Unscrew it until a steady jet of water emerges or you hear a hissing noise. If you hear hissing, the radiator contained air and this prevented the water filling the entire radiator. Allow the air to escape and then re-tighten the bleed valve as soon as you see a steady stream of water.

Identify the feed and return pipe valves at the base of the radiator. The feed pipe is the one that got hot first when you switched on the heating. There is a valve where it enters the radiator. If the radiator fails to heat, or is too cold, but the feed pipe is hot, there is a problem with the valve. Using an adjustable wrench, very gently turn the valve counterclockwise to increase the flow of water into the radiator and make it hotter. Turn it clockwise to reduce the flow of water and make the radiator cooler.

Check the return valve where the other pipe joins the radiator. This has either a thermostatic or manual control valve. In a thermostatic valve, a small wax plug expands and contracts depending on the room temperature, automatically controlling the water flow. Conventional control valves also regulate the water flow. Adjust them until the radiator heats the room to the desired temperature. Turning counterclockwise gives more heat; clockwise gives less heat.


Make all adjustments gradually and allow the room time to warm up or cool down before making further adjustments. If valves look heavily corroded be very gentle when attempting to turn them. If they won't move, either call a plumber or be ready to replace the valve if it snaps off as you apply more force. If you have to keep bleeding air from the radiator, then air must be entering the system. Call a plumber.


Do not work on very hot radiators. High temperature water and steam can inflict severe burns. Always switch off the heating pump before working on radiators. This allows air to settle and greatly reduces the pressure in the pipes. Radiator water may contain a black iron compound. This can stain walls and carpets if not cleaned up quickly. Increasing the heat in one radiator leaves less heat to be shared between the other radiators.

Things You'll Need

  • Radiator bleeding key
  • Adjustable wrench
  • Small container
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About the Author

David Robinson has written professionally since 2000. He is a Fellow of the Royal Geographical Society and the Royal Meteorological Society. He has written for the "Telegraph" and "Guardian" newspapers in the U.K., government publications, websites, magazines and school textbooks. He holds an honors Bachelor of Arts in geography and education and a teaching certificate from Durham University, England.