How to Repressurise Your Boiler — Step by Step | Halo Heating

Why Does Boiler Pressure Drop?

Your boiler operates as a sealed, pressurised system. Over time — especially after bleeding radiators or if there's a minor leak — the pressure can drop below the minimum required level (usually 1 bar). When this happens, most modern boilers will display a fault code and stop heating your home.

Common reasons for low pressure include:

**Bleeding radiators** — releasing air also releases a small amount of water

**Slow system leaks** — often at radiator valves, joints, or the boiler itself

**Faulty pressure relief valve** — releasing pressure into the drain

What You'll Need

Your boiler manual (to locate the filling loop)

A flathead or Phillips screwdriver (some filling loops require this)

A cloth to catch any drips

Step-by-Step: How to Repressurise Your Boiler

Step 1: Turn Off the Boiler

Switch your boiler off completely and allow it to cool down for at least 30 minutes before starting. Working on a hot system is both dangerous and inaccurate.

Step 2: Locate the Filling Loop

The filling loop is usually a silver or grey braided hose with valves at each end, located underneath the boiler. Some boilers have an internal filling loop — check your manual if you can't see an external one.

Step 3: Open Both Filling Loop Valves

Turn the valves slowly (usually a quarter-turn) to open them. You should hear water entering the system. Keep an eye on the pressure gauge.

Step 4: Watch the Pressure Gauge

Allow the pressure to rise to approximately 1.2–1.5 bar (cold). This is the ideal operating range. Do not allow it to exceed 1.5 bar before closing the valves.

Step 5: Close the Valves

Once you reach the correct pressure, close both valves firmly. Disconnect the filling loop hose if it's a removable type and store it safely.

Step 6: Restart the Boiler

Switch the boiler back on. The fault code should clear, and your heating should resume normally. If the boiler continues to display a pressure fault, call an engineer.

When Pressure Keeps Dropping

If you find yourself repressurising more than once a month, you likely have a leak somewhere in the system. This could be a pinhole leak in a pipe, a dripping radiator valve, or a failing boiler component. Do not ignore persistent pressure loss.

Call Halo Heating on 01483 676108 and our Gas Safe engineers will locate and fix the source of the problem quickly.

How to Repressurise Your Boiler — Step by Step