To flush a hot water heating system, follow these steps:
1. Turn the system off and close the water feed valve to the boiler. Let the system cool.
2. Connect a hose to the drain valve that’s located on the bottom of the boiler, and run the hose to an indoor or outdoor drain.
3. Open the air vent on the highest radiator to break the vacuum.
4. Now open the drain on the boiler and let the entire system drain.
5. Once the system drains, close the radiator valve, open the feed valve, and flush water through the boiler until the water runs clean.
6. Close the drain valve on the boiler and let the system refill.
7. Start the boiler (even if it’s summer) to purge air out of the system.

Finally, consult your owner’s manual for more specific instructions before you start. If you feel uncomfortable attempting this maintenance, let your service contractor do it the first time while you watch and take notes. Depending on how old and dirty the system is, you may want the contractor to “power flush” it using special chemicals.

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