Boiler
F.22
The F.22 error code on a Worcester Bosch boiler indicates low water pressure — one of the most common boiler faults in the UK and, in many cases, something you can resolve yourself in minutes.
What does this error mean?
Your Worcester Bosch boiler continuously monitors the water pressure inside the central heating system. When that pressure drops below approximately 0.5 bar, the boiler locks out and displays F.22 as a safety measure to prevent damage to the heat exchanger and pump. Normal operating pressure should sit between 1.0 and 1.5 bar when the system is cold.
Est. repair cost
£0 if re-pressurising solves it; £150–£350 for a Gas Safe engineer to fix a leak, PRV, or expansion vessel; £400–£600+ for internal component failure
🔍 Likely causes
🛠️ Step-by-step fix
Check the pressure gauge on your boiler — if it reads below 1.0 bar (or is in the red zone), low pressure is confirmed as the cause.
Locate the filling loop — usually a flexible braided hose with one or two valves beneath or beside the boiler. If you cannot find it, check your boiler manual or the Worcester Bosch website for your specific model.
Open the filling loop valve(s) slowly and watch the pressure gauge rise. Stop when it reaches 1.2–1.5 bar. Do not overfill — pressure above 2.5 bar can trigger the PRV.
Close the filling loop valve(s) fully, then press the reset button on your boiler (usually marked with a flame or circular arrow symbol) and wait for it to restart.
Monitor the pressure over the next 24–48 hours. If it drops again below 1.0 bar, you have a leak somewhere in the system and must call a Gas Safe registered engineer — do not keep re-pressurising as a fix.
If you see water dripping from a pipe outside your home (the PRV discharge pipe), or if you cannot locate a visible leak but pressure keeps dropping, stop here and call a professional.
📞 When to call a professional
Call a Gas Safe registered engineer immediately if pressure keeps dropping after you’ve re-pressurised, if you can see any water leaking from the boiler or pipework, or if the PRV discharge pipe outside your property is dripping. Tell the engineer: ‘My Worcester Bosch boiler is showing F.22, I’ve re-pressurised it but it keeps losing pressure’ — this gives them a clear starting point and may save diagnostic time.
⚖️ Repair or replace?
Most F.22 repairs involve fixing a leak or replacing a faulty PRV or expansion vessel, typically costing £150–£350 with a Gas Safe engineer in the UK. If your boiler is over 10–12 years old and requires a significant repair such as a new heat exchanger (£400–£600+), replacement with a new A-rated combi boiler (typically £1,800–£2,800 installed) is usually the smarter investment. For boilers under 8 years old in otherwise good condition, repair is almost always the right call.