Glow-worm F22 Fault Code: Low Water Pressure Guide
The F22 fault code on a Glow-worm boiler means the water pressure in your system has dropped below the normal range of 1 to 1.5 bar. Like the Ideal F1 and Vaillant F.22, this is a common fault that you can often fix yourself.
What the F22 fault code means
The F22 code is a low water pressure warning. Your boiler needs water pressure between 1.0 and 1.5 bar to operate safely. When the pressure drops below this range, the boiler shuts down to protect itself from damage.
Possible causes of the F22 fault
- Water pressure below 1 bar — The system has lost water and needs repressurising.
- Problem with the water pressure sensor — The sensor may be faulty and giving incorrect readings.
- Loose, disconnected, or faulty wiring — The wiring to the pump or pressure sensor may be damaged.
- Water pressure sensor faulty — The sensor itself may need replacing.
- Pump not working properly — On open vented boilers only, the pump may not be circulating water.
- Internal expansion vessel faulty — The expansion vessel may have lost its charge.
Can you fix it yourself?
Yes — if the pressure is genuinely low. Here's how:
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Check the pressure gauge — Look at the pressure gauge on your boiler. If the needle is below 1.0 bar, the system needs repressurising.
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Repressurise the system — Use the filling loop (usually a silver braided hose with two valves, located near the boiler). Slowly open both valves and watch the pressure gauge. When it reads between 1.0 and 1.5 bar, close both valves.
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Reset the boiler — After repressurising, reset the boiler. The F22 code should clear.
When the pressure is above 1 bar
If your pressure gauge reads above 1.0 bar and the F22 code is still showing, the problem is likely not low pressure but a faulty sensor or wiring issue. In this case, call a Gas Safe registered engineer — do not attempt to fix the pressure sensor yourself.
When the pressure keeps dropping
If you repressurise the system and the pressure drops again, you have a leak somewhere in the system. This could be:
- A leaking radiator or valve
- A pinhole leak in pipework
- A leak inside the boiler
- A faulty expansion vessel
A Gas Safe registered engineer will need to find and repair the leak.
When to call a professional
Call a Gas Safe registered engineer if:
- The pressure is above 1 bar but the F22 code persists
- The pressure keeps dropping after repressurising
- You can see water leaking from the boiler or pipework
- You're not confident repressurising the system
Need help with your Glow-worm boiler?
Sanju's Heating covers Newbury, Basingstoke and Reading. We're Gas Safe registered and can diagnose and repair Glow-worm F22 faults with transparent pricing.
Call us on 01635 74 50 40 or book online at sanjusheating.co.uk/book
Check our full Glow-worm fault code guide for help with other Glow-worm error codes.
