Though less common in modern homes, boilers remain HVAC workhorses, particularly in older homes without traditional ductwork. These systems, which are known for their energy efficiency and durability, require proper maintenance to ensure their longevity. This guide delves into the critical process of draining a boiler, a critical task for HVAC professionals that, if not done correctly, can pose risks of injury and potential water damage. 



Step 1: Perform a quick flush to remove sediment 

Before turning off the boiler, perform a quick flush to remove any sediment that has become lodged in the valve. Connect a garden hose to the drain valve and use short bursts of water to dislodge the sediment. If a significant amount of sediment blows out, repeat the process. 

Step 2: Shut Down Your System 

Turn off the power source for both gas and electric boilers. Turn off the water using the cold-water pipe valve or the main water supply valve. Confirm that there is no hot water in the faucets and that the pipes have completely cooled down. 

Step 3: Turn on the drain valve and flush the tank 

Connect a drain hose, open the boiler’s drain valve, and release the vacuum in the tank. Allow water to flow while slightly moving the hot water pipe to the side. Flush the tank in stages by turning on and off the water while leaving the hot water pipe disconnected. 

Step 4: Refill Your Hot Water Heater 

Disconnect the hose, close the drain valve, and reconnect the hot water pipe after draining. Restart the water, ensuring that air exits the lines by running a hot water faucet. Turn off the faucet once only hot water is flowing.

Step 5: Restart the water heater and inspect the drain valve 

Restore power to electric boilers; relight the pilot light in gas boilers. Check the drain valve for proper closure and address any leaks as soon as possible. 


Every six to twelve months, residential boilers benefit from a complete flush. This prevents corrosion and leaks by removing sediment and sludge. Regular draining improves efficiency by reducing the workload on the boiler and resulting in energy savings. 


After draining, be wary of potential leaks. Prepare a cap in case the valve does not completely close. Before turning the water back on, consider upgrading the plastic valve. Draining at least every six to twelve months is recommended by industry experts to maintain boiler efficiency and extend its lifespan by preventing sediment buildup. 


Regular maintenance, including draining every 6 to 12 months, is essential for a boiler’s optimal performance and longevity. Neglecting this aspect may result in energy waste, increased costs, and plumbing emergencies. Professional maintenance and repairs, no matter how minor the issue appears to be, are required to keep your boiler in top working order. 


If you need assistance or have questions about boilers, Green City Heating and Air Conditioning is here to assist in Kent, Auburn, and the surrounding areas. Get a quote or schedule a service today or contact us at (206) 249-9772.

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