Error F.22

Safety precautions:

1. Before you start, turn the boiler off and allow it to cool. Avoid working on a hot boiler. Turn off mains power to the boiler if you will be touching electrical components (only qualified persons should expose wiring).

2. If you see water pooling, corrosion or smell gas, do not attempt repairs; turn off the gas and water supply and call a professional immediately.

3. Do not attempt to bypass safety devices or operate the boiler if you do not understand the steps.

Initial homeowner checks you can do:

1. Look at the boiler display or pressure gauge. Note the pressure reading; F.22 commonly appears when pressure is below about 0.4 bar. Cold system target is typically around 1–1.5 bar (check your manual for exact value).

2. Check for obvious leaks: pipe joints, radiators, boiler underside, valves, and the pressure relief/drain pipe. If you find a leak, isolate the water if possible and call a Gas Safe engineer.

3. If you recently bled radiators or had plumbing work, that is a likely reason for pressure loss.

Step-by-step diagnostic and fix (repressurise and basic checks):

1. Turn the boiler OFF and let it cool. Locate the filling loop: either two small grey/metal valves beneath the boiler (integrated loop) or an external flexible hose with two isolation valves.

2. Confirm the filling loop valves are fully closed before starting. Place a towel underneath in case of drips.

3. Slowly open the filling loop valves/handles one at a time to admit mains water into the system. Watch the boiler pressure gauge or display while you open the valves. Do not leave the filling loop open unattended.

4. Increase pressure slowly to around 1.0–1.5 bar cold. Once stable in that range, close both filling loop valves fully. If you have an external removable hose, re-remove or re-secure it if recommended by the manufacturer.

5. If you over-pressurised the system (pressure >2.5 bar), bleed a radiator to reduce pressure: open radiator bleed key slowly until pressure falls back to the target and re-check gauge.

6. Turn the boiler back on and reset it if required. Many Vaillant boilers clear the code once pressure is restored; if a reset is necessary, consult your manual (typical reset involves pressing and holding the reset/menu button for a few seconds). Watch for the F.22 to clear and for normal operation to resume.

7. Bleed radiators after repressurising if you hear gurgling or suspect trapped air. Re-check pressure after bleeding, then top up again if needed and re-close the filling loop.

When to call a professional (must-call scenarios):

1. If the F.22 returns soon after repressurising (pressure drops quickly or frequently) — this usually indicates a leak, failing pressure relief valve, faulty expansion vessel, or other internal fault that needs a Gas Safe registered engineer.

2. If you find a visible leak, water around the boiler, or discharge from the pressure relief pipe.

3. If repressurising does not clear the fault or the boiler shows other error codes, or you suspect the pump is defective or the pump lead/wiring is faulty.

4. If you are not comfortable isolating/operating the filling loop or working near the boiler’s wiring and gas connections.

Additional diagnostic notes:

1. If the system pressure falls very slowly over months, the system may simply need occasional topping-up; if it drops rapidly, suspect a leak or component failure. Keep a log of how often you need to top up.

2. Persistent faults related to pump operation (no flow, pump noise, or electrical issues) or repeated overheat warnings require trained inspection; do not attempt to replace pumps, sensors or internal wiring unless you are a registered engineer.

Final advice:

Repressurising often resolves a one-off F.22 event, but recurring faults or any sign of leak/damage mean you should contact a Gas Safe registered heating engineer. They can perform safe diagnostics, test the expansion vessel, pressure sensor, pump and valves, and carry out any necessary repairs or replacements.