Why Is My Boiler Losing Pressure?

If your boiler refuses to fire up and the pressure gauge is sitting below 1 bar often in the red zone — you’re likely dealing with low boiler pressure.

Low pressure means there isn’t enough water circulating through your heating system, so the boiler shuts down as a safety precaution.

You may notice:

• Heating not working properly

• Radiators staying cold

• Boiler pressure below 1 bar

• Hot water issues

• The boiler failing to start altogether

The good news is that low boiler pressure is one of the most common and easiest boiler issues to fix.

Signs Your Boiler Pressure Is Low

• Heating not working

• Pressure gauge below 1 bar

• Radiators cold or only partially heating

• Boiler displaying a fault code

• No hot water

Common Causes of Low Boiler Pressure

The most common causes include:

• Small leaks in the heating system

• Bleeding radiators without topping pressure back up

• Natural pressure loss over time

• Faulty pressure relief valves

• System component issues

How To Repressurise Your Boiler

1. Turn the boiler off

Allow the boiler to cool down before touching anything.

2. Check the pressure gauge

If the pressure is below 1 bar, it is too low. Most boilers should sit between 1 and 2 bar.

3. Find the filling loop

This is usually a flexible silver hose underneath the boiler with a valve at each end. Some boilers use a built-in filling key instead.

4. Open the valves slowly

Turn the valves gently until you hear water entering the system.

5. Watch the pressure gauge

Allow the pressure to rise slowly to around 1.2–1.5 bar.

6. Close the valves firmly

Once the pressure reaches the correct level, close both valves fully.

7. Turn the boiler back on

Reset the boiler if required.

8. Check everything is working

Your heating and hot water should return to normal.

9. Look for visible leaks

Check underneath the boiler and nearby pipework for any drips or damp patches.

10. Call an engineer if the pressure drops again

If the pressure falls again within a few days, there may be a hidden leak or internal fault.

Safety Note

Do not attempt to repressurise your boiler if:

• The pressure is above 2.5 bar

• You cannot find the filling loop

• You are unsure what you are doing

Always contact a Gas Safe registered engineer if you are uncertain.

When To Call An Engineer

You should contact a heating engineer if:

• The pressure keeps dropping

• You notice visible leaks

• The pressure gauge is above 2.5 bar

• The boiler still will not work after repressurising

• You are unsure how to safely top the system up

How To Prevent Low Boiler Pressure

You can help prevent pressure problems by:

• Booking annual boiler servicing

• Checking pressure regularly

• Bleeding radiators correctly

• Keeping an eye out for leaks

• Maintaining your heating system properly

Need Help With Your Boiler?

If your boiler pressure keeps dropping, don’t ignore it — it could indicate a hidden leak or system fault.

RF Henderson Heating offers:

• Boiler repairs

• Annual boiler servicing

• Boiler care plans

• Emergency heating support

📞 Call 01670 735 577 or contact us online to arrange an engineer visit.