The pressure gauge (sometimes called a manometer) on your boiler tells you the water pressure in the sealed central heating circuit. Understanding it helps you spot problems early and avoid unnecessary engineer call-outs.
Where to find it
Most modern combi and system boilers display pressure either on a physical gauge (a round dial) or a digital readout on the boiler display. Some newer models show pressure on an app via the smart thermostat.
What the readings mean
- Below 0.5 bar: Too low — boiler will likely lock out and stop working. Re-pressurise immediately.
- 1.0–1.5 bar (cold system): Correct — this is the target range
- 1.5–2.0 bar (hot system): Normal — pressure rises when heated
- Above 2.5 bar: Too high — the pressure relief valve may open. Do not re-pressurise further. Call an engineer.
- Above 3.0 bar: Dangerously high — turn boiler off and call engineer immediately
Why pressure changes
Pressure drops when: water escapes through a leak, or the system is bled. Pressure rises when: the system heats up (normal), or the expansion vessel has failed (requires engineer).
When to top up yourself
Pressure below 1 bar: safe to re-pressurise using the filling loop. See our re-pressurisation guide for step-by-step instructions.
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