Error F.22

Safety precautions:

- If you are unsure at any point, stop and call a Gas Safe-registered engineer. Working on boilers and gas appliances can be dangerous.

- Before you start, turn the boiler to standby or switch it off at the boiler switch or isolator and allow it to cool if it has been running. Follow the manufacturer’s safety instructions in the manual.

- Never leave the filling loop or valves open unattended. Do not over-pressurise the system.

Initial checks a homeowner can do:

1. Check the pressure gauge on the front of the boiler. Note the cold pressure (aim for about 1.0–1.5 bar; check your manual).

2. Look for visible signs of leaks around the boiler, pipes, radiator valves, or underfloor manifolds. Check floor and ceiling for damp patches.

3. Think about recent activities: were radiators bled, was any plumbing work done, or was the system drained recently?

4. Locate the filling loop: either two small grey or chrome valves under the boiler (integral filling loop) or a flexible braided hose with two isolation valves (external filling loop).

Specific diagnostic and fix steps (re-pressurising):

1. Ensure boiler is off or at standby and the system is cool. Keep the boiler power isolated if you prefer, but you may need to watch the pressure gauge while topping up.

2. Identify the two filling loop valves. Confirm they are closed before you begin (usually perpendicular to the pipe when closed).

3. Slowly open the first valve (usually only a partial turn if it is a tap) then slowly open the second valve to allow mains water into the central heating system. Keep your hand on the valve so you can quickly close it.

4. Watch the pressure gauge closely. Stop adding water when the cold system pressure reaches about 1.0–1.5 bar (many sources recommend 1.2–1.5 bar). Do not exceed 2.0–2.5 bar when cold; the boiler will raise pressure when it heats.

5. Close both filling loop valves fully and remove/replace any blanking cap on an external loop. Make sure the valves are isolated so the mains cannot feed the system continuously.

6. If you accidentally over-pressurise, bleed a radiator until the pressure returns to the correct range, checking the boiler gauge after each bleed.

7. Turn the boiler back on and observe. If the fault does not clear automatically, follow the boiler manual to perform a reset (hold reset button as directed). The F.22 should clear once pressure is correct.

8. Monitor the pressure over the next few days. If the pressure drops slowly over months it may be normal top-up; if it drops quickly or repeatedly you likely have a leak or a faulty component.

When to call a professional (Gas Safe engineer):

- The F.22 fault returns within days or weeks after repressurising.

- You find any visible leaks or damp related to the heating system.

- The boiler will not repressurise, the pressure gauge appears faulty, or the boiler displays additional or persistent faults.

- You suspect failure of components such as the expansion vessel, pressure relief valve (PRV), pump or pressure sensor.

- You are not confident to follow the steps safely.

Important safety notes:

- Do not attempt to repair gas or sealed pressure components yourself unless you are a qualified engineer.

- Never leave the filling loop valves open after topping up—this can cause over-pressurisation and damage.

- If in doubt, switch the boiler off and arrange a Gas Safe-registered engineer to inspect and repair the system.