How to Increase Boiler Pressure and Clear Error Codes Step-by-Step
One of the most frequent winter heating issues occurs when the boiler suddenly stops firing, leaving your home without hot water or heating, while an error code flashes on screen—such as F22 (Vaillant), E10 (Baxi), or EA (Junkers/Bosch). In over 70% of cases, the root cause is a simple drop in closed-circuit water pressure below the safety threshold (0.5 - 0.8 bar). This practical guide explains how to safely repressurise your heating circuit in 3 minutes without tools.
Step 1: Check the Pressure Gauge Reading
Look at the front display or analog pressure dial of your boiler. Correct cold pressure should sit stably between 1.2 and 1.5 bar.
If the needle points below 0.8 bar, the internal low-pressure safety switch triggers a shutdown to protect the primary heat exchanger from dry boiling damage.
Step 2: Locate the Filling Loop Under the Boiler
Crouch underneath the boiler casing where copper pipes connect. Look for the filling tap or flexible braided loop linking cold mains water to the central heating return pipe.
It is typically a small plastic or brass valve (often black, blue, or a winged turn-cock). On Junkers/Bosch it is frequently a retractable knob; on Vaillant, a small lever tap; and on Saunier Duval, a dual blue or quarter-turn mechanism.
Step 3: Open the Valve Slowly Until Reaching 1.2 to 1.4 Bar
Gently turn the valve anticlockwise. You will hear incoming water flowing into the heating circuit.
Watch the pressure gauge closely as the needle rises. Once it reaches between 1.2 and 1.4 bar, immediately close the tap tightly by turning clockwise. Never exceed 1.8 bar cold, otherwise when radiators heat up, water expands past 3 bar and discharges through the pressure relief valve.
Step 4: Reset the Boiler to Clear the Fault Code
Once operating pressure is restored, the safety sensor detects sufficient water. On modern digital boilers, the error code usually clears automatically within 30 seconds.
If the lockout persists, press the Reset button (often marked 'R' or a crossed flame icon) for 3 to 5 seconds. The boiler will restart its ignition sequence and resume heating.
For any 24h technical emergency, our team is dispatched immediately in mobile workshop vans fully equipped to resolve boiler breakdowns on-site: call 936 94 00 23.
FAQ
What happens if I accidentally overpressurise the boiler to 2.5 or 3 bar?
Modern boilers have a safety relief valve calibrated to 3 bar. To lower the pressure back down, bleed a radiator with a radiator key or coin into a small container until the pressure gauge returns to 1.2 - 1.4 bar.
Why does my boiler keep losing pressure every week?
A central heating system is a sealed loop. Ongoing pressure loss usually indicates: 1) a dripping pressure relief valve caused by a depressurised expansion vessel, 2) weeping radiator valves or bleed nipples, or 3) a concealed pipe leak.
What if the filling loop valve is jammed and will not turn?
Never force a plastic filling tap with pliers, as it can snap and cause immediate flooding under your boiler. If seized by limescale, call our emergency technicians dispatched in mobile workshop vans at 936 94 00 23.