How to drain a home radiator

Updated February 21, 2017

Draining a home radiator is necessary when you have to change a radiator or take a malfunctioning one in for service. A radiant heating system works by circulating hot water through a network of pipes and radiators in your house. As the water passes through the radiator, it heats up the radiator fins, which warm the surrounding air. The water is then passed back to the boiler to be reheated and start the cycle again.

Turn off the power for the heater. You can do this either at the heater or at the circuit breaker that controls the heating power.

To protect the floor, place a dropcloth or sheet of plastic underneath the radiator you will be draining.

Shut off the inlet valves at either end of the heater. In most installations, one of these will be a thermostat-type knob that you can turn by hand, while the other will have to be closed with a wrench or pliers.

Open the bleed screw at the top of the radiator with the bleed wrench.

Locate the drain valve for the radiator. In most cases, the drain valve will be installed on either the inlet or outlet valve. It will be mounted horizontally rather than vertically like the inlet or outlet valve. Place a bowl or container under the valve and open it with a wrench. Allow the bowl to fill. Close the valve and empty the bowl when needed. If you don't have a drain valve, you can drain the radiator by emptying it through the union joint.

To drain the radiator by emptying it through the union joint, use a pair of wrenches to disconnect the radiator from the union joints where the radiator meets the inlet and outlet valves. Use one wrench to hold the valve steady while you unscrew the union joint with the other wrench. Keeping the valve steady helps prevent the pipes from being damaged.

Unscrew the radiator from any brackets holding it to the wall. Lift up on the radiator to remove.


Allow the water inside the heating system to cool for an hour or so if it is in use prior to draining.

Things You'll Need

  • Plastic sheet/dropcloth
  • Wrench
  • Bleeding wrench
  • Bowl/container
  • Pliers
  • Screwdriver
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About the Author

Nathan McGinty started writing in 1995. He has a Bachelor of Science in communications from the University of Texas at Austin and a Master of Arts in international journalism from City University, London. He has worked in the technology industry for more than 20 years, in positions ranging from tech support to marketing.