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Boiler Pressure too High

Boiler Pressure too High? Get it Back Under Control!

The pressure on your boiler pressure is a variable. A small increase or decrease in pressure is nothing to worry about. However, a boiler can’t function properly when operating far outside the normal range. What happens when the system becomes over-pressurised? How can you tell when the pressure is too low or too high? What are the main reasons for this? How can you fix it yourself? Find out right here!

Why Boiler Pressure Matters

Each boiler system consists of pipes and other components that are filled with water and air. The balance between these two elements defines boiler pressure. If the pressure is adequate, the system will be pumping hot water around the pipes. If it is inadequate, the system won’t be able to heat the cold water running through radiators.

How Do You Check the Pressure on a Boiler?

You should be able to see a pressure gauge on the front of your boiler. Typically, boilers can provide readings between 0 and 4 bar while 1 to 1.5 bar hit the sweet spot. Readings below 1 and above 4 are major red flags, but even 2.5 bar is too high for a boiler. Once the boiler reaches 3 bar it shuts itself automatically, which is a useful safety feature.

Is High Boiler Pressure Dangerous?

No, high boiler pressure is not dangerous, except if the relief valve is damaged or clogged. However, this can have a major affect on the efficiency of the appliance.

Most Common Reasons for High Boiler Pressure and Easy Fixes

1. Too much water in the system

Switch the boiler off. If your boiler pressure gauge displays a reading above 1.5 bar, that is a telltale sign there is too much water in the system. If this is the case, bleed your radiators to drain water from the system.

You’ll need a tool to unscrew the valve on the radiator – a radiator key would be great. Untwist the valve slowly and listen for the sound of the air escaping. As the air escapes, it will make way for some water to flow out as well. Check the pressure gauge after you let out a small amount of water. If the pressure is still above average, check the second most common reason for high boiler pressure.

2. Malfunctioning parts

A faulty filling loop or pressure release valve (PRV) could be the reason for the change in pressure within your boiler. The PRV automatically releases water from the boiler when it accumulates too much pressure. When the boiler can’t supply you with hot water, the PRV (copper pipe) is almost 100% to blame. There is no way to fix this yourself. Instead, call a certified engineer to fix it for you.

Check the black taps underneath your boiler and the filling loop once in a while. Make sure everything is tightly closed, otherwise the boiler will start generating pressure. If the filling loop taps are partially open, call an expert to inspect the problem.


Pressure-related issues can point to a number of problems with your boiler. If you need professional advice, one of our Gas Safe engineers can check your boiler and fix the malfunction or you can submit a quote for a new boiler. If you need more help, don’t hesitate – contact us today!

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