How to Bleed the Pressure From a Steam Boiler

You must bleed radiators yearly.

A steam boiler uses steam-filled radiators to heat a home. Yearly, before each heating season, you must bleed the boiler system to ensure you maintain the proper pressure inside the closed system. Each radiator in your home has a bleeder valve. The bleeder valve is the valve that allows you to expel air trapped in the closed circuit. Air trapped in the circuit prevents proper water pressure and keeps the radiators from heating at their full capabilities.

Things You'll Need

• Bleeder key or needle-nose pliers
• Cup

Instructions

1. Map out the radiators in your home to create a plan of attack. You must start with the radiator closest to the furnace and work sequentially to the radiator located the furthest away from the furnace. This does not mean the physical distance from the furnace. It means the first radiator mounted to the water pipes that come out of the furnace. To determine this, you must trace the water lines that come out of the furnace and connect to the radiators. It is not vital that you go in sequence but it makes the task easier as you expel less air at each individual radiator.

2. Locate the bleeder valve at the top of the radiator. Place a cup directly under the valve and then turn the valve counterclockwise slowly until you hear air escaping the valve.

3. Turn the valve closed again once water starts to stream out of the valve. Water will first start to spit out with the air. Do not turn off the valve until water streams out without any air.

4. Repeat this process with each radiator in the home.

Tips & Warnings

• When expelling air, you may have an issue where the furnace loses the pressure needed to expel air. You will know when this happens because the sound of air flowing out of the valve will stop and you will not have any water coming out. If this happens, close the valve and wait for the furnace to turn on and then turn back off. This will build up pressure and allow you to complete the process. This usually happens when you reach the higher levels of the home where it requires more pressure to heat the radiators.

References

• Old House Journal; How To Take Care of Your Radiators; Dan Holohan