Modern residential boiler systems are very reliable, but if and when they do break down, finding the underlying cause of the problem can be a challenge. If your boiler keeps switching itself off before it has properly heated your home or created enough hot water for your needs, the problem may be caused by low water pressure in your boiler system.

What Causes Low Water Pressure In Boilers?

Residential boilers function by heating cold water, which enters the system through a filling loop. The heated water is then directed to bathtubs, sinks, and other appliances that use hot water, and channeled through the radiators in your home to provide ambient heating. For the hot water to reach your radiators and appliances, it must be pressurized. 

Ordinarily, your boiler system maintains water pressure by piping water into the system from your home's main supply, then shutting off the supply once optimal water pressure is achieved, creating a closed loop. If the valves that control water flow into your boiler system malfunction, your boiler may lose water pressure. 

Your boiler system may also be suffering from low water pressure if you have bled your home's radiators recently. Bleeding a radiator removes unwanted air pockets from the boiler's closed-loop, which can undermine efficiency if they become trapped in radiators. However, bleeding too much air out of the system can lead to a drop in water pressure.

Leaks in your boiler system can also cause persistent problems with insufficient water pressure, as water leaks out of the boiler's closed-loop system faster than it can be replaced. A leaky boiler can also cause serious water damage in your home. Leaks can occur in and around the boiler itself or in the system's pipes and radiators.

Why Does Low Water Pressure Cause Boilers To Switch Off?

Low water pressure causes water to stay inside the boiler's heat exchanger for too long, causing it to overheat and boil. Boiling water can seriously damage a heat exchanger, as well as other components inside your boiler.

To prevent this from occurring, boilers are fitted with pressure sensors, which monitor the system's water pressure and automatically switch the system off if they drop too low. The system is also fitted with a temperature sensor that will deactivate the boiler if the heat exchanger gets too hot.

If your boiler system switches itself off and cannot be reactivated, the low-pressure sensor has probably been tripped. It will not reactivate until water pressure levels have been restored. The boiler system may also need to be reset to reactivate the pressure sensor.

If your boiler switches itself off but reactivates itself a short time later, the water pressure in your system may be fluctuating. This can be caused by leaks, blockages in pipes, sediment deposits in your boiler's heating tank, and other problems.

What Should You Do About Low Water Pressure In Boilers?

If your boiler has a digital readout screen, it will probably show an error message if the boiler is deactivating due to low pressure and/or overheating problems. Older models may be fitted with a hydraulic pressure gauge, with a red bar indicating insufficient water pressure. If the gauge's needle is hovering in the red, you have a low water pressure problem.

If you know how to operate your boiler's filling loop, you can attempt to fix the problem yourself by adding more water to the system to pressurize it. Make sure the boiler is deactivated and has completely cooled down before you attempt this.

Unfortunately, repressurizing the system may not work if the boiler is malfunctioning due to leaks, electrical problems, or issues with your system's valves and/or circulator pump. If adding more water to the system doesn't fix the problem, or you don't know how to use your boiler's filling loop, call in a professional boiler repair service to find and fix the underlying problem for you.