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Why is my boiler pressure too high?

If your boiler pressure is too high, it could be due to a number of reasons. Read more on how to reduce and fix your boiler’s pressure.

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Why is my boiler pressure too high?

Your boiler pressure needs to be just right if it’s going to be able to pump hot water around your home safely. Too high and it could cause significant damage to your heating system,

There are a few reasons why your boiler pressure is too high, including having too much water in the system through to faulty parts.

Here we look what you can do to reduce the pressure as well as reasons why it might be happening.

What boiler pressure is too high?

A combi boiler’s pressure gauge is typically found on the front of the appliance and should sit comfortably between 1 and 1.5 bar of pressure (or the green section). This level should be maintained and checked regularly in order for the central heating system to work efficiently throughout the year.

If it sits in the red portion - or beyond 2.5 - some adjustments or further checks are required to bring things to the right bar of pressure. Some gauges have an LCD screen display, which will display the pressure as you click through the on-screen options.

If the reading is between 3-4 it’s likely that the boiler will shut itself down as an internal safety precaution.

Boiler pressure is high when heating is on

A slightly higher reading while your boiler is in operation is normal due to the water demand being paced on the system. So, something nearer the 2 mark is nothing to worry about.

However, if something between 3-4 is your usual operation pressure then you should raise this with a professional engineer.

If you’re seeing high pressure readings on an all too regular basis, it may be worth considering a brand new boiler, particularly if your current one is around 10 years old.

How to reduce your boiler pressure

While adjusting your boiler pressure may seem scary at first, trust us, it’s relatively quick and simple.

Here’s the steps you need to take:

  • Switch off your boiler and wait for the heating system to cool
  • Identify and check the boiler pressure gauge
  • If it’s above 2 bars, you’ll need to reduce the pressure
  • Ensure the filling loop or relief valve is tightly closed
  • Bleed your radiators to release trapped air from the heating system
  • Check to see if the boiler pressure returns to its correct setting

Boiler Pressure still too high?

If your boiler pressure is still high after you’ve bled your radiators, there could be a more serious underlying issue.

  • Expansion vessel needs repressurising
  • Fault with the filling loop
  • Fault with pressure release valve
  • Fault with the diverter valve
  • Fault with the filling loop

To resolve these issues, you’re going to need the help of a qualified Gas Safe Engineer. So, if you keep getting a high pressure reading, give one a call.

Can I also increase my boiler pressure?

Of course. If there isn’t enough pressure in your system, you’ll likely be suffering from an inefficient and under-performing system.

Raising the pressure means you’ll have to get hands-on with your boiler. But don’t worry, it’s a simple and safe enough process to do on your own.

Before you do though, it’s worth checking your user manual, or even the manufacturer’s website for any step-by-step instructions or even blog videos.

  • Switch your boiler off and let it completely cool.
  • Find your boilers filling loop. This is a flexible hose found underneath your boiler with a small valve at each end, make sure both ends of the hose are secured and attached to the two valves.
  • Use the valves handles on either side, turn them clockwise and open the valves. This will then allow the cold mains water into the system, and you'll hear it filling up the system.
  • The pressure will now increase, so pay attention to the pressure gauge until it gets to the 1.5 bar mark. You'll then want to start closing both valves by turning the valves counter-clockwise.
  • Turn the boiler back on and reset your boiler if necessary. 

Common error codes for boiler brands with high pressure

 To confirm whether your boiler’s pressure is too high, you should also get an error code displayed on the front of the unit. Pretty handy.

These differ for each manufacturer:

  • Worcester Bosch boiler pressure too highLikely error codes: E9, A1, 224V, 1065B, 2970B
  • Vaillant boiler pressure too highLikely error codes: F.12, F.74, F.75, S.41
  • Ideal boiler pressure too highLikely error codes: F1 – Ideal boilers tend to communicate in English and simply display written messages about pressure issues which is, well… Ideal.
  • Potterton boiler pressure too highLikely error codes: E117, E430
  • Baxi boiler pressure too highLikely error codes: 117, E430, E117, E125, E193

Boiler pressure still too high?

If your boiler pressure is too high, we have a number of other useful guides in our online Advice Centre that could help you out, including a run down of common boiler faults, and tips on resetting your boiler.

Book a boiler repair now