Radiator / heating symptoms / boiler pressure
Why does my boiler pressure keep dropping?
Start with the observable symptom. This page explains possible causes; it is not a diagnosis.
Repeated pressure loss can follow bleeding, but it may also indicate a leak or a boiler-system fault. Check the gauge and visible pipework safely, follow the manufacturer’s instructions once if appropriate, and call a qualified heating engineer if pressure falls again.
Start with the pattern.
The pressure gauge or display repeatedly drops below the boiler’s recommended range.
Possible causes, not a diagnosis.
- Water was lost after bleeding a radiator.
- A radiator, pipe, underfloor circuit or pressure-relief route may be leaking.
- The expansion vessel or another boiler component may need professional attention.
Check what is safe to observe.
- 01
Read the pressure when the system is cool and compare it with the boiler manual.
- 02
Look for drips, damp patches or discharge outside without touching hot pipework.
- 03
Note whether pressure falls quickly or only after heating cycles or bleeding.
Take the smallest useful step.
- Follow the manufacturer’s safe repressurising instructions only if you know the filling system.
- Turn the boiler off and let it cool before any approved pressure adjustment.
- Keep a record of pressure readings and any visible leak.
- Do not keep topping up pressure to hide a repeated drop.
- Do not remove the boiler casing or repair gas components.
- Call a qualified heating engineer when pressure drops again, falls quickly or there is any leak.
- Use an appropriately licensed gas professional in the UK (Gas Safe registered engineer) for work on a gas boiler.
Professional requirements and rental responsibilities vary by location. Use the qualified local professional or housing authority that applies where you live.
UK example: Gas Safe RegisterWhy this page says that.
This page separates an observable symptom from possible causes and keeps the recommended action within a safe household boundary.