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Boiler Pressure Too Low? Here’s What to Do
A dropping pressure gauge is one of the most common boiler worries — and often one of the easiest to fix. Here is how to top it up safely.
Omar Haddad
Service Manager03 Jul 2026Updated: 03 Jul 20264 min read
Key takeaways
Reading time — 4 min
Expert reviewed — Practical guidance from our heating team
If your boiler pressure gauge has slipped into the red and your heating feels weak, low pressure is usually to blame. In most cases you can restore it yourself in a couple of minutes.
What the gauge should read
A healthy system sits between 1 and 1.5 bar when cold, rising slightly as it heats. Anything below 1 bar can stop the boiler firing to protect itself.
How to repressurise
- Locate the filling loop — a silver braided hose beneath the boiler.
- Open both valves slowly and watch the gauge climb toward 1.5 bar.
- Close the valves as soon as you reach the target.
- Restart the boiler and check the heating fires normally.
When to worry
If pressure keeps dropping after repeated top-ups, there is likely a leak in the system or a failing expansion vessel. That is a job for a Gas Safe engineer, not another refill.