How to Drain & Refill a Hot Water Heating System

Written by nathan mcginty
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How to Drain & Refill a Hot Water Heating System
Drain and refill your hot water heating system to keep it operating efficiently. (white radiator image by Ekaterina Sidorenko from

Before old man winter comes around, you should take the time to drain and refill your hot water heating system. This will clear out any debris that might be floating around inside the pipes and keep your system operating at its most efficient. These types of systems are drained through the boiler and refilled at the same location. The procedure for how to drain and refill a hot water heating system isn't hard, and once you complete it successfully, you'll be able to do it for yourself every year, without having to spend money on a plumber.

Skill level:

Things you need

  • Radiator bleed screw
  • Garden hose
  • Newspapers

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  1. 1

    Shut off the power for the boiler that controls the hot water heating system. You can turn the power off on the boiler by flipping the switch to the "Off" position, or you can switch the circuit off for the boiler at the main circuit. Turn off the heating system.

  2. 2

    Go to the radiator unit located the highest and furthest away from the boiler. If this is a two story house with the radiator located at the rear, for example, go to a radiator located upstairs towards the front of the building. Loosen the bleed screw on the radiator with the radiator bleed key.

  3. 3

    Go to the boiler. Attach the end of a garden hose to the boiler drain outlet, which is typically located at the bottom of the unit. Turn off the water supply valve, usually located at the top of the radiator, by turning the knob clockwise. Open up the boiler pressure relief valve. Run the other end of the garden hose to a sink or drain.

  4. 4

    Open up the drain valve on the radiator. Allow the water inside to drain out of the system through the hose. Close the drain valve once the radiator is empty.

  5. 5

    Close the bleed screw on the radiator you opened in Step 2.

  6. 6

    Open up the water supply valve for the boiler. Restore power to the boiler and allow it to fill up to the appropriate pressure reading. Some boilers may do this automatically. Turn on the heating system.

  7. 7

    Go back up to the same radiator you used in Step 2. Place the newspaper on the floor beneath the radiator. Open the bleed screw. Keep it open until water seeps out of the bleed hole. Close the screw.

Tips and warnings

  • Some boilers may not have an attachment for a garden hose. In that case, you will have to drain the boiler into a bucket or other container.
  • The water in the hot water heating system can be quite hot. Use caution when emptying.

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