How to Reduce Your Boiler Pressure

Learn how to safely reduce boiler pressure in your central heating system. Follow our step-by-step guide to prevent damage and ensure a safe and cosy home.

Boiler pressure is one of those things we don't think about until it becomes a problem. 

One minute, your central heating system is warming your home; the next, you wonder why the pressure gauge is in the red. 

If you’re dealing with high boiler pressure, you’ve come to the right place.

In this guide, we look at how to reduce your boiler pressure and some reasons why a boiler’s pressure may have dropped.

Understanding boiler pressure

Boiler pressure is a measure of the force at which water is pumped around your heating system. Most boilers operate efficiently within a pressure range of 1 to 2 bars. If the boiler pressure is too high or too low, it can affect the performance and safety of your heating system. 

Here’s a handy guide from the experts at JustFix to help you keep things under control.

Why is high boiler pressure a problem?

High boiler pressure can lead to a host of issues that will stop your home from running smoothly:

  • Leaking water: Excess pressure can cause water to leak from the boiler.
  • Faulty valves: High pressure might damage the pressure relief valve and other components.
  • Reduced efficiency: Your boiler's efficiency can take a hit, leading to higher energy bills.
  • Safety risks: Excess pressure can be dangerous and may cause your boiler to shut down automatically.

Boiler service

How to reduce boiler pressure: Steps to take at home

Here are some steps to reduce boiler pressure safely and effectively at home. If the problem persists after these steps, you may need to appoint a heating and gas engineer to take a look. 

1. Check the pressure gauge

The boiler's pressure gauge is your first point of reference. It should typically read between 1 and 2 bars. If it’s higher or lower, it's time to take action.

2. Bleed the radiators

Bleeding radiators is a simple way to release trapped air and reduce pressure:

  1. Turn off the boiler: Ensure the heating system is off and cool.
  2. Use a radiator key: Insert the radiator key into the bleed valve.
  3. Open the valve: Turn the key counterclockwise until you hear a hissing sound.
  4. Collect excess water: Use a container underneath the valve to catch any water.
  5. Close the valve: Once the hissing stops, tighten the valve.

3. Use the pressure relief valve

The pressure relief valve is designed to release excess pressure automatically. However, if it’s faulty or stuck, you might need to release pressure manually:

  1. Locate the valve: Check your boiler's manual to find the pressure relief valve.
  2. Turn the valve: Carefully turn the valve to release water and reduce pressure.
  3. Monitor the gauge: Keep an eye on the pressure gauge and stop when it reaches the normal range.

4. Drain the system

If the pressure remains high, you may need to drain some water from the system:

  1. Turn off the boiler: Ensure the boiler is off and cool.
  2. Attach a hose: Connect a hose to the drain cock.
  3. Open the valve: The drain valve releases water until the pressure drops.
  4. Close the valve: Close the valve once the pressure is within the normal range.

5. Check for faulty components

Sometimes, high pressure can be due to a faulty expansion vessel or pressure relief valve. If these components are damaged, you may need to replace them. 

Always consult a Gas Safe engineer for repairs involving these critical parts.


When to call a heating and gas engineer

While many pressure issues can be resolved at home, some situations require professional help. 

Contact a Gas Safe registered engineer if:

  • The pressure gauge consistently reads high despite your efforts.
  • You notice water leakage from the boiler or pressure relief valve.
  • The boiler frequently shuts down due to high pressure.
  • There are error codes displayed on your boiler's control panel.

The cost of a heating and gas engineers

If your boiler needs immediate attention, a fully qualified JustFix heating and gas engineer costs only £110 + VAT per hour.

Some providers charge more based on location, boiler type, and demand, but this isn’t how we work at JustFix. When you book a heating and gas engineer with us, you know exactly what you’ll be paying in advance, so there are no surprises or hidden costs to worry about.

Due to the nature of boiler problems, if your appliance requires new parts, there may be an additional charge for materials. However, your Fixer will square this with you before proceeding. 

Common causes of high boiler pressure

Several factors can contribute to high boiler pressure:

  • Overfilled heating system: Pressure can build up if too much water is added via the filling loop.
  • Faulty expansion vessel: This component absorbs the expansion of heated water, and if it’s faulty, pressure can rise.
  • Trapped air: Air trapped in radiators can cause pressure to increase.


The danger of low boiler pressure

While high pressure is a common concern, low boiler pressure can also be problematic. Low pressure can lead to:

  • Inefficient heating: The boiler may struggle to heat your home effectively.
  • Frequent shutdowns: The boiler may shut down to prevent damage.
  • System damage: Prolonged low pressure can cause wear and tear on boiler components.

If you suspect low boiler pressure, check the gauge and refer to your boiler’s manual for instructions on how to increase the pressure safely.

Preventive measures to maintain normal boiler pressure

To keep your boiler pressure consistent and avoid future issues, consider these preventive steps:

  • Regular maintenance: Schedule annual maintenance with a qualified engineer to keep your boiler in top condition.
  • Monitor pressure: Regularly check the boiler’s pressure gauge, especially during colder months.
  • Bleed radiators: Periodically bleed your radiators to release trapped air and maintain efficient heating.
  • Check the filling loop: Ensure the filling loop is closed after topping up the boiler to prevent overfilling.

Consider a service plan

For greater peace of mind, you can look into getting a service or care plan alongside your boiler. These often include a yearly service and access to priority appointments, so they can work out cheaper than paying for one-off callouts every time you need one.

JustFix offers plumbing and heating service plans starting at just £15 per month. These plans cover your annual boiler service, heating system safety checks, priority appointments, and more.

Sign up for a HappyHome plan from JustFix and take the pressure off you and your boiler.


Book a heating and gas engineer with JustFix

Keeping your boiler pressure in check is essential for the efficient and safe operation of your central heating system. At JustFix, we're not about high costs or low-quality services.

Our teams of Fixers work nationwide to provide you with professionals for fair, fixed prices. It's pretty simple, really. We're surprised no one's done it before.

When you book online with us, we'll match you with a qualified heating and gas engineer local to you who can come and sort out your boiler pressure at a time that suits you.

FAQs about boiler pressure

Does bleeding a radiator reduce boiler pressure?

Yes, bleeding a radiator can help reduce boiler pressure. Trapped air in the radiators can cause pressure imbalances within the heating system. By bleeding the radiators, you release this trapped air, which can lower the overall system pressure. To do this, turn off your boiler, use a radiator key to open the bleed valve, and let the air escape until water begins to flow out. Close the valve once the air is fully released. This process helps to restore balanced pressure within the system and can improve the efficiency of your heating system. 

Always check the pressure gauge after bleeding to ensure it is within the normal range.

Is 2.5 bar too high for a boiler?

Yes, 2.5 bar is generally considered too high for a boiler. Most boilers are designed to operate efficiently within a pressure range of 1 to 2 bars. A pressure reading of 2.5 bar indicates that the system is under excessive pressure, which can lead to leaks, faulty components, and even safety risks. If your boiler's pressure consistently reads 2.5 bar or higher, take steps to reduce the pressure and consult a heating and gas engineer.

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