Why Is My Boiler Losing Pressure?

Boilers are ... pretty awesome! They're a longstanding form of home heat, and they're energy-efficient, have a long lifespan and come in a variety of models to choose from. Despite its reliability, though, a boiler can require maintenance or encounter problems periodically. In fact, nothing is worse than turning on your heat only to realize your home isn’t heating up and your boiler is losing pressure.

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Fortunately, there are a few things you can do to prevent this from happening.

What Are Some Reasons for My Boiler Losing Pressure?

Boilers heat water, which turns to steam or stays as a liquid, depending on the type of boiler you have. The pressure inside the boiler sends the water or steam throughout your home to a radiator or radiant floor system, where it gives off heat. It’s common to encounter low boiler pressure over time. However, if the pressure drops suddenly or the boiler keeps losing pressure, there’s typically a problem within the system. Some of the most common reasons for a boiler losing pressure include:

• Age of the system. Worn and corroded parts or accumulated debris inside an older system may be the cause of a boiler slowly losing pressure.

• Leaks. The most common reason for a boiler losing pressure is a leak within the system. Check for small drips coming from the radiator, from the valves or along the pipes. The smallest leak can cause water to escape and result in pressure loss.

• Natural changes in pressure. As water heats and cools, it naturally causes changes in pressure. Major changes can indicate a bigger issue within the system.

• Broken expansion vessel. The expansion vessel keeps the water pressure inside the boiler stable while the water heats and cools. When the vessel fails, it can cause the system pressure to drop suddenly.

• Faulty pressure relief valve. The pressure relief valve allows the pressurized fluid inside the boiler to escape safely. Problems with this valve can cause pressure to drop.

• Bleeding radiators. It’s important to bleed your radiators of excess air every few months to ensure the system is working properly. If water is allowed to escape, it can cause a loss in pressure.

Can a Boiler Lose Pressure Without a Leak?

If you notice your boiler losing pressure but there's no leak, consider other causes.

• Air within the pipes. Air bubbles can form inside your boiler pipes over time, causing the pressure to fluctuate.

• Broken parts. Like any heating system, parts can wear down over time. Worn and broken parts can cause pressure changes.

• Adjustments. While it’s not as common, it’s possible pressure wasn’t set correctly after a recent maintenance call. In this case, contact a repairman to check for issues.

Sometimes leaks are hidden under your floorboards or within walls. If you can’t find the reason for a pressure drop, you may need to contact a professional to check for hidden leaks.

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• It’s Too Hot in Here! How to Turn Down Your Radiator

• How Much Does It Cost to Install or Replace a Boiler?

How Do I Fix My Boiler That Keeps Losing Pressure?

A boiler losing pressure doesn’t have to be a cause for alarm. In most cases, you can repressurize the system on your own and get it back on track.

• Turn off the system. Start by turning off your boiler and waiting for the system to cool down.

• Bleed your radiators. Start with the radiator furthest from your boiler. Use a radiator key to open the valve and bleed the radiator. You’ll notice a hissing noise as the air escapes. When water starts to come out, turn the key to close the valve. Continue the process until you’ve bled all the radiators in your home.

• Check the pressure. Check the pressure gauge on your boiler. If the pressure is too low, proceed to pressurize the system.

• Repressurize the boiler. Locate the filling loop or the silver, flexible hose on your boiler. Open the valve on the hose to allow water into the system while watching the pressure valve. You should hear water flowing. When the pressure reaches your manufacturer’s recommended level, close the valve. Most systems operate at 1.0 to 1.5 amounts of pressure.

• Turn the boiler on. Check the pressure on your system again. If it doesn’t return to normal, it may be time to contact a professional.