Why Is My Boiler Losing Pressure?
- 2 days ago
- 2 min read
A boiler losing pressure is a common issue in many homes and can lead to heating problems, such as radiators not warming up properly or the boiler switching off completely. Understanding the cause can help you decide whether it’s a simple fix or a job for a professional plumber.
What Boiler Pressure Should Be?
Most modern boilers should run at around 1.0 to 1.5 bar when cold. If the pressure drops below 1 bar, the system may stop working correctly.
Common Reasons for Pressure Loss
1. Water Leak in the System
A small leak in your heating system is one of the most common causes. This could be:
A leaking pipe joint
A radiator valve leak
A hidden leak under floors or behind walls
2. Bleeding Radiators
If you’ve recently bled your radiators, you may have released air and water from the system, which can lower pressure.
3. Faulty Pressure Relief Valve
If the pressure relief valve is damaged or sticking, it may be letting water escape from the system.
4. Expansion Vessel Issue
A faulty expansion vessel can cause unstable pressure and repeated drops.
5. Recently Refilled System
Sometimes pressure drops after topping up the system as air works its way through the system.
How to Top Up Boiler Pressure
Most boilers have a filling loop:
Switch off the boiler and let it cool
Open the filling loop valves slowly
Watch the pressure gauge rise to around 1.2–1.5 bar
Close valves and restart the boiler
⚠️ Only top up pressure if you are confident — repeated pressure loss usually indicates a fault.
When to Call a Plumber
You should contact a professional if:
Pressure keeps dropping after topping up
You can’t find any visible leaks
Boiler is shutting down frequently
You hear hissing or dripping noises
Need Help With Boiler Pressure Issues?
Blue Flame Plumbing & Heating provides fast boiler repairs and heating system diagnostics across Nottingham and surrounding areas. If your boiler keeps losing pressure, we can quickly find and fix the cause.
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