How to Re-pressurise Your Boiler

If your boiler display shows a pressure reading below 1 bar (or you see a low pressure warning light), re-pressurising is usually something you can do yourself — no engineer needed.

What is the correct boiler pressure?

For a cold system (boiler not running): 1 to 1.5 bar. When hot and running: 1.5 to 2 bar. Pressure naturally rises slightly when the system heats up. Below 0.5 bar: boiler will likely lock out and stop working.

How to top up pressure (most boilers)

1. Turn the boiler off and let it cool for at least 30 minutes
2. Find the filling loop — usually a silver braided hose under the boiler connecting two pipes, each with a valve
3. Open both valves (usually by turning the slotted screw 90° with a flathead screwdriver)
4. Watch the pressure gauge rise — stop when it reaches 1.2–1.5 bar
5. Close both valves immediately — do not over-pressurise
6. Turn the boiler back on

If pressure keeps dropping

Occasional top-ups (every few months) are normal as sealed systems can lose small amounts of pressure over time. If you need to top up monthly or more, there is likely a leak in the system. Call us — we'll find and fix it as part of a service visit.

Important: never open the pressure relief valve

The pressure relief valve (PRV) releases pressure if it gets dangerously high. If yours is dripping, call an engineer — it needs replacing, not manually opening further.