This guide explains:
- Why boiler pressure drops
- How to top up your boiler pressure (step by step)
- When to call a heating engineer
Why Is My Boiler Losing Pressure?
Modern boilers work on a sealed, pressurised system. If the pressure falls too low, the boiler will often shut down for safety.
Common Causes of Low Boiler Pressure
- A leak in the heating system (radiators, pipes, valves, or the boiler itself)
- Radiators recently bled (releasing air lowers pressure)
- Faulty pressure relief valve or expansion vessel
- Slow, hidden leaks under floors or behind walls
If you find you are topping up boiler pressure frequently, this usually indicates a leak or a faulty component, and you should contact a professional.
How to Top Up Boiler Pressure
Always check your boiler manual before starting. Only top up if you are confident with the process. If in doubt, call a Gas Safe registered engineer.
Step-by-Step Guide to Repressurising
- Turn off the boiler and allow it to cool for at least 30 minutes.
- Locate the pressure gauge, usually beneath the boiler. When cold, the pressure should read between 1.0 and 1.5 bar.
- Find the filling loop valves — these are normally underneath the boiler. Some boilers use a built-in filling key or lever instead.
- Slowly open both valves to let water into the system. You should hear water flow.
- Watch the pressure gauge rise to between 1.2 and 1.5 bar.
- Close both valves tightly once the correct pressure is reached.
- Switch the boiler back on and reset it if necessary.
- Check for leaks and wipe up any water spills.
Still Losing Pressure After Topping Up?
If the pressure keeps dropping, the cause may be:
- A slow leak in your heating system
- An expansion vessel that needs recharging
- A pressure relief valve stuck open
- Internal boiler seals or components that are worn or failing
At this point, it is best to book a heating engineer to diagnose and safely repair the fault.
What Not to Do
- Do not keep repressurising the boiler every few days — this hides a bigger problem
- Do not attempt to open or tamper with the boiler casing — this is for Gas Safe engineers only
- Do not ignore repeated fault codes or constant low pressure
Signs You Need Professional Repair
- Boiler pressure drops daily or weekly
- Visible leaks around radiators or pipework
- Constant low-pressure error codes (such as F22 or E119)
- No hot water or heating
- Boiler making unusual noises when starting
Book a Professional Boiler Repair
Our Gas Safe engineers are available across the UK to diagnose and repair pressure loss issues quickly and safely.
We work with all major boiler brands, including Worcester Bosch, Vaillant, Ideal, Baxi, Glow-worm, Viessmann, Alpha, Vokèra, Ariston, and Ferroli.
Areas We Cover
We provide nationwide support, including:
- London, Birmingham, Leeds, Glasgow, Cardiff, Manchester, Newcastle
- Towns and villages across England, Scotland, Wales, and Northern Ireland
- Rural communities and remote areas
Same-day and next-day appointments are often available.
Customer Feedback
“Topped up my boiler using this guide, but it kept dropping. The engineer found a leaking radiator pipe — now fixed and no more issues.”
– Lisa, Southampton
“Easy to follow step-by-step. Got my boiler running again in 10 minutes.”
– James, Nottingham
Need Help With Boiler Pressure Problems?
Do not let low boiler pressure leave you without heating or hot water. Our engineers are ready to help across the UK.
