How to Drain and Refill My Steam Boiler

Even though boilers are one of the oldest forms of household heating available, many of today’s homeowners aren’t familiar with properly maintaining their boilers, especially steam systems. However, maintenance doesn’t have to be a mystery.

Understanding how your boiler works and how to best maintain it can save you money on utility costs, increase your boiler’s lifespan, and ensure your family is warm and comfortable all winter.

One of the most common maintenance tasks is draining and refilling your steam boiler to eliminate minerals and sediment that build up in the system. While boiler sludge isn’t toxic, allowing this buildup to remain can clog the boiler tubes and interfere with your boiler's ability to efficiently heat your home. You won’t need any specialized equipment or have to worry about exposure to toxins when you drain and fill your steam boiler.

Every homeowner with a steam boiler should know how to drain and fill their system, which entails the following steps:

• Shut the system off
• Open the drain valve and flush out sediment
• Refill and restart boiler

Need help from a professional boiler tech?

If you have any questions or need assistance with any part of the drain-and-refill process, call Ranshaw Plumbing & Heating today at (718) 767-0707. We have over 60 years of experience maintaining, repairing, and installing steam boilers and can perform most routine tune-ups and other maintenance tasks in about one hour.

The first step in draining your steam boiler is completely shutting off the system. You can shut off the boiler by either turning off its power (emergency switch) or switching the thermostat to the off position. Shutting the boiler off will stop the system from producing steam and building up pressure, so when you open the drain valve (see next step), water will not burst out with excessive force.

Next, you will need to locate the boiler drain valve, which is typically a round knob below the sight glass (the long tube that displays the boiler water level) at the bottom of the boiler. Position a bucket directly underneath the valve. Before opening the drain valve, make sure the water in the gauge glass is still. If the water is still moving, allow more time for the boiler to cool down before opening the valve.

To open the valve and drain the boiler, rotate the valve slowly counter-clockwise.

How much water should be drained from your steam boiler?

Draining your boiler until the water becomes clear is recommended. The amount of water you will need to drain will vary. If you are draining your boiler on a regular basis (weekly), you’ll likely need to drain less water as opposed to a boiler that is drained infrequently.

Now that your boiler has been drained, it’s time to close the drain valve and refill the system.

If your boiler is equipped with an automatic water feeder…Your system will automatically refill with water when the boiler is turned on again.

To manually refill your boiler…You will need to open the boiler fill valve and refill the boiler until the water in the gauge glass reaches the correct level, which is halfway to 2/3 full. You can turn the system on once you have refilled your boiler.

Now that you’re an expert at draining and refilling your boiler, your next question might be, how often is draining a steam boiler required?

During the heating season, when you're using your boiler on a regular basis, you should drain and refill your steam boiler system once a week.

You can cut back to once a month during the summer when the boiler is not in use.

Ranshaw’s highly-trained boiler technicians can perform a thorough 14-point boiler maintenance service in less than one hour in most cases. We service and repair all boiler makes and models, and because we know your time and money are valuable, we offer a 100% satisfaction guarantee. When you choose us, you’re choosing a family-owned business backed by 1-year labor warranties and hundreds of 5-star reviews.

Call us today at (718) 767-0707 during business hours or visit our online portal to schedule service.