What Should Boiler Pressure Be When Heating Is On?

Your boiler must be able to circulate hot water in order to keep your home warm. It requires the proper amount of pressure to accomplish this. You’ll know what pressure your boiler should be and what to do if it’s too low or too high after reading this article.

The Ideal Boiler Pressure

On the front of most gas boilers, there is a pressure gauge that displays the current pressure. Some pressure gauges include a single needle, with red spots on the dial indicating low and high pressure. Others have two needles, one red to indicate where the pressure should be and the other black to indicate where it is. Some boilers have an LCD panel that shows the pressure and flashes or displays an error message if the pressure is too high or too low.

  • When the Heat Is Off: The ideal pressure for when the heat is off is between 1 and 1.5 bar on a boiler pressure gauge.
  • When the Heat is On: The ideal pressure for when the heat is on is about 2 bars on a boiler pressure gauge.

How to Check your Boiler Pressure With a Pressure Gauge

Most of the boilers we see on the market currently are the combi and system type. These machines always have a built-in boiler pressure gauge, allowing you to check the pressure whenever you like.


The built-in systems either feature a digital or a hydraulic pressure gauge. Either way, taking a quick look at the panel will quickly reveal whether the pressure is within the expected pressure levels.

Why Do Boilers Have Higher Pressure When the Central Heating System is On?

As you already know, slightly high boiler pressure is okay when the heating is on. The reason for the acceptable high boiler pressure while the central heating is working is that when the water heats, the radiators and pipes expand. When your heating system deals with this water expansion, it is only natural for the pressure to increase.

If you notice the boiler pressure is high consistently, it may be down to two things.

Too Much Water In The System: This could be the case if you’ve just added water to your system owing to low pressure. Bleeding your radiator is a straightforward procedure. This allows some of the water to escape, lowering the pressure.

Boiler Issue: If bleeding your radiators doesn’t work, it’s possible that one of the boiler’s parts is broken. To investigate, contact a Gas Safe Registered engineer.

Steps to Reduce Boiler Pressure

It’s important to stress that each boiler make is different and the first thing you should do is consult the manual. Now, with that said here are some steps that you can take to reduce boiler pressures that are fairly common across the different brands and models.

To re-pressurize your boiler, you’ll need to use a filling loop to let more water into the system. These can be integrated into your boiler or purchased separately. The design and filling technique for filling loops can vary, but here’s the general guide:

  • Turn off your boiler.
  • Please take a look at the filling loop valves and ensure that they are completely shut.
  • Allow the system to cool before allowing the boiler to release pressure through the radiators.
  • Check the pressure gauge and if the pressure is too high after the previous steps, continue bleeding your radiators.
  • Turn on Your boiler when the pressure gauge comes to a safe reading.

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Last Updated on November 7, 2021

Frequently Asked Questions

Will having irregular gas safe pressure cause problems in the hot water supply?

Whether you have low boiler pressure or see that your boiler’s pressure is too high, you will certainly feel an issue in the hot water supply. You keep an eye for the boiler heats since that will make the expansion vessel and the entire boiler shut off, disrupting the water heating system.

What happens if the boiler pressure is too high?

Too high or too low boiler pressure is not good. However, it is not very dangerous either. With the pressure relief valve and the lockout system, your boiler will sense when there is a need to bleed the radiators and do the needful.

How often should I check my boiler pressure?

Once a month, check your boiler pressure to ensure it isn’t too high or too low. If the pressure has gone below 1 bar after bleeding your radiators, you should inspect it. It’s a good idea to monitor boiler pressure shortly before the heating season begins to ensure that your boiler is in good working order for the winter.

Is the pressure in the boiler continuing to rise?

Even after you’ve double-checked your valves and bled your radiators, does your boiler pressure continue to rise? This could potentially be the result of a more serious problem.

Request that your engineer examine your boiler’s pressure release valves or vents, as these may be the source of the problem if they aren’t functioning properly. They’re there to relieve any excess pressure and keep the pressure in your boiler from climbing too high. If the increased pressure has nowhere to go, it can be dangerous to your boiler’s health, so get professional assistance as soon as possible.

David Thompson

Author: David Thompson

Dave has been involved in the UK building sector for over 3 decades and has developed a particular interest in energy efficiency in the home.

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