Is Your Boiler Losing Pressure? A Boiler Pressure Problem Could Stop Your Central Heating From Working

Have you started to notice your boiler losing pressure?

Has your heating or hot water suddenly stopped working?

A gradual or sudden drop in boiler pressure can have many causes including:

  • A Water Leak Inside Your boiler
  • A Water Leak somewhere in your Central Heating System
  • Faulty Expansion Vessel
  • Damaged Pressure Relief valve
  • Recently bled radiators

What Is Boiler Pressure?

Boiler pressure is the pressure of the hot water inside your central heating system.

The water inside your heating system is pressurised to allow the hot water to flow efficiently throughout your central heating installation – keeping your heating working and home warm!

Keeping your boiler pressure between 1 and 2 bar is critical to ensure your boiler and heating system work effectively, to help avoid any breakdowns and problems. 

How can I Check My Boiler Pressure Is Low?

You can check the pressure of your boiler using your boiler pressure guage – which maybe a digital display or an analogue guage.

The boiler pressure guage is located either inside or underneath the boiler, it may also be located near the filling loop.

A boiler pressure less than 1 bar is too low.

If you suspect a pressure problem with your boiler system then you will also need to check if the boiler pressure is to high. If the pressure is too high your heating could also stop working and your boiler may also display a pressure error fault code.

Common Fault Codes For A Boiler Losing Pressure

Viessmann Boiler Fault Codes

Fault CodeFault
C1Differential air pressure
B9, ED, F0, F-ED, F-EE, F-E5, F-EC, F-EF, F-FD, F-FFMaximum Pressure Limiter Fault
F5Faulty Gas Pressure
EE and EFFaulty Air Pressure
0FService Required

Worcester Bosch Boiler Fault Codes

Fault CodeFault
E9Safety limiter
A1Dry pump
F0Major internal error
CE 207Low water pressure present
H07Low water pressure that is impacting performance
1065 BPressure sensor is defective
1970 BSudden, rapid pressure drop

Ideal Boiler Fault Codes

Fault CodeFault
F1low water pressure

Other Boiler Manufacturer Fault Codes Displayed When Their Boilers Lose Pressure

ManufacturerFault Codes
BaxiE119 / E118 H.02 – .06 / E.02 – .07 / 125
FerrolliF35 / F37 / A37
Glow WormF22 / F9 / F24

How To Repressurise A Boiler That Is Losing Pressure

Follow these step by step instructions on how to repressurise your boiler yourself:

Step 1) Switch off the boiler at the thermostat and allow it to cool – this is perhaps the most important stage, and should not be skipped or rushed.

Step 2) Double check the boiler to ensure that both ends of the filling loop are securely attached, and in good condition.

Step 3) Open both of the valves SLOWLY – using a screwdriver. This allows the cold mains water to enter the system, and should be audible if you listen closely.

Step 4)  Watch the pressure gauge; when it hits the 1.5 bar, you are good to go.

Step 5) When the dial hits 1.5, close both valves

Step 6) Switch the boiler back on, and hit the reset button

Boiler Pressure FAQ’s

In most cases, the issues occur when you have low boiler pressure. If this happens, the system can completely cut out, leaving your heating not working. In the majority of modern boilers – known as a ‘combi boiler’ – the pressure is kept even and maintained by a filling loop, which connects to the cold water pipe.

Understanding the most common causes of pressure loss can help you identify and repair the cause.

There are usually one of five reasons behind a drop in boiler pressure:

  • Boiler pump or Heat Exchanger Leaking
  • A leak on your Central heating System
  • Damaged Expansion Vessel
  • Faulty Pressure Relief Valve
  • Recently Bled Radiators


Yes, a boiler can lose pressure without a leak. Boiler pressure loss can occur for various reasons, and not all of them involve a physical water leak.

Some common causes of boiler pressure loss without a visible leak include bleeding radiators or automatic air vents releasing pressure from your boiler.

The good news is that low pressure in a boiler is rarely dangerous. The more significant risk is when the boiler pressure is high. When a combi boiler has persistent high pressure, there is a considerable risk of damage to the internal components.

However, this does not mean that regular issues with low pressure in a boiler should be ignored as it will adversely effect boiler efficiency.

Regular pressure gauge readings are useful in monitoring your boiler pressure.

Even a tiny leak can cause extensive water damage to your property over time, so if you cannot find the leak’s source and the problem returns quickly, then call ADI Leak Detection as soon as possible.

The source of a leak causing a pressure drop could be underfloor heating pipework located under the screed or floorboards of your property or even above ground joints at radiators and towel rails. The tiniest pinholes can develop into larger leaks over time and usually start at the joints of copper pipework as the joints erode over time.

If it is your first time topping up your combi boiler, then it is an easy mistake to add too much water. Virtually all modern boilers have a water pressure sensor which is designed to regulate the pressure, alongside a pressure release valve and an internal expansion vessel. The pressure sensor is designed to prevent any damage occurring to the pump itself.

However, if you do not want to rely on these systems, then another quick and easy fix would be to bleed the radiators. If the high-pressure problem persists, you need to call a Local Gas Safe Engineer. 

When To Call In A Professional Water Leak Detection Company Regarding The Loss Of Boiler Pressure

Repetitive repressurizing of your boiler shouldn’t be ignored – its a sign of a fault with your boiler or central heating system.

Here at ADI Leak Detection, our team is highly skilled and qualified in detecting and repairing water leaks. Our experienced team are Central Heating Leak Detection Specialists, have the equipment and knowledge to trace a leak on your heating system causing your boiler pressure loss.

Leak Detection Company For Low Boiler Pressure

Adrian Morgan

Adrain Morgan CIPHE RP RHP is the founder & Managing Director of ADI Pro Leak Ltd. Adrian is also the Head Plumbing, Heating & Leak Detection engineer at ADI Leak Detection.

Adrian CIPHE RP RHP is proud to be registered with the Chartered Institute of Plumbing & Heating Engineering, a Registered Plumber and a Registered Heating Professional.