How to Reduce Boiler Pressure

Boiler pressure refers to the strength of water running within the sealed central heating system.

It naturally increases as the water heats up. 

Over time, operating at high pressure can cause your boiler to stop working.

It can even damage your home.

Below, we've given a guide on diagnosing what's wrong, including:

• 3 common causes of high boiler pressure
• 5 steps for checking and reducing your pressure (without any assistance)
• Expert insights on keeping your boiler safe and efficient.

Important note: Boiler repairs can be hazardous. Only readjust your boiler pressure in certain circumstances. Whilst this guide helps you identify ways to reduce pressure, you should always consult a Gas Safe registered engineer for internal checks to ensure your home's safety. 

Checking boiler pressure

Start by working out the correct pressure for your boiler.

Most conventional modern boilers have a digital pressure reading or bar indicator display.

Older boilers have round hydraulic pressure gauges with a dial and needle, which can usually be found underneath the boiler.

In either case, pressure typically sits within a normal range of 1.2 - 1.5 bars (including in a cold, switched-off boiler).

Your boiler's pressure is too high if the needle/bar reading has moved above 2 (or into the red zone). 

You might also notice that the heating system has shut down or a flashing error appears on the LCD display.

Causes of high boiler pressure

In the boiler industry, it's well-known that small details often create big problems. 

Ignoring a minor pressure fluctuation can rapidly escalate into a costly emergency.

Here are the most common culprits:

1. Excess water in the central heating system

The most common cause of high pressure is too much water in the system.

Overfilling often occurs after the pressure is adjusted from being too low. 

If the valve or filling loop has been accidentally left open, it will continuously draw in too much water.

2. Expansion of boiler parts

This particular problem happens naturally over time.

As your hot water heats up, the pressure in the boiler increases. 

Heat makes things expand. So, the water and parts inside swell up a bit.

3. Faulty parts and leaky valves

Your high pressure could be caused by:

• A faulty pressure release valve
• A broken filling loop
• A failing expansion vessel
• Leaking valves.

Incorrect air levels in the expansion vessel can cause over-pressure.

If you find water on or around the pressure release valve or pipes, it could mean the system is compromised.

Cost to fix

A faulty part is not something you can fix yourself. 

You'll usually pay for the replacement part, plus the engineer's fee to fit it.

5 steps to reduce boiler pressure yourself

In the majority of cases, anything above two bars is an indication that your boiler pressure is too high. 

There are a few simple steps you can try to safely lower it.

Step 1: Switch off your boiler and let it cool

Switch your boiler off and wait for the system to completely cool down before attempting any fixes.

Step 2: Check the filling loop

Check if the filling loop is tightly closed. You can secure it by turning it clockwise.

Step 3: Check the relief valve

Make sure that your pressure relief valve is securely closed.

Step 4: Bleed the radiators

Bleed the radiators to release any trapped air and excess water from the system. 

Use a radiator key to carefully let out the pressure, catching any dripping water in a cloth.

Step 5: Recheck the pressure gauge

Recheck the pressure gauge on the front or underneath your boiler. 

Check that your pressure has returned to 1.1-5 bars.

Get to "know normal"

How do you keep a system running safely and out of emergency mode? 

Get to "know normal" for your boiler.

Do frequent visual checks. Keep an eye on your pressure display, look around for minor leaks, and listen for unusual noises from your boiler. 

Good boiler maintenance is the best way to prevent breakdowns and extend your equipments' lifespan.

Consider boiler cover

Is the boiler pressure continuing to rise?

Can't fix it yourself? It's time to call a professional.

Need the peace of mind to know you're protected against any sudden, expensive boiler repair costs?

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• Over 5,000 gas safe engineers across the UK
• A UK-based call centre open 24 hours a day
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• An annual boiler service and safety check included.

For instant protection, call our friendly team on 0330 223 4422 and never worry about unexpected boiler repair costs again.