Advice
Combi Boiler Pressure: The Complete Guide
Everything you need to understand the pressure gauge.
System pressure is one of the few things homeowners can safely monitor and adjust on a combi boiler. Most run around 1–1.5 bar when cold, rising a little when hot. Understanding the gauge helps you spot leaks early and keep the boiler running.
Here's how pressure works and how to top up safely.
Pressure essentials
- Aim for ~1–1.5 bar when the system is cold
- Pressure rises slightly when the system is hot — normal
- Below ~1 bar, many boilers reduce or stop heating
- Top up slowly via the filling loop per your manual
- Repeated loss means a leak — book an investigation
When to call
If pressure keeps dropping after topping up, or climbs into the red and the relief valve discharges, the cause (a leak or expansion-vessel fault) needs a technician.
This is not a DIY repair
Combi boilers are gas-fired appliances regulated under the BC Safety Standards Act. Opening the unit, touching the gas valve, or working on the flue without a valid BC gas-fitter licence is both unsafe and illegal. Diagnosing the fault is helpful — fixing it should always be left to a certified technician.
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