How to Fix a Glow-worm F22 Fault Code

The Glow-worm F22 fault code usually means your boiler has low water pressure. Without enough pressure, the heating system cannot circulate water correctly, so the boiler shuts down to protect itself.

In many cases, the pressure simply needs topping up. However, if the pressure keeps falling, there's usually an underlying problem that needs repairing rather than repeatedly refilling the system. If you're seeing a different error, our guide to Glow-worm boiler fault codes explains what each code means and when professional repairs are needed.

What Does the Glow-worm F22 Fault Code Mean?

The Glow-worm F22 fault indicates low water pressure within your central heating system. You may also notice a pressure reading such as 0.3 bar on the display. Most Glow-worm boilers operate best at around 1.0 to 1.5 bar, although you should always check your model's manual.

If the pressure is well below this level, the boiler prevents normal operation until the issue is resolved.

Why Is My Glow-worm Boiler Showing F22?

The most common causes include:

• Low system pressure.
• A leak in the boiler or heating pipework.
• Air trapped after bleeding radiators.
• Blockages caused by sludge or debris.

Pressure often drops gradually over time. If it suddenly falls or you need to top it up every few weeks, there is usually a fault that should be investigated.

Signs of a Glow-worm F22 Fault

Besides the error code itself, you may notice:

• Cold or partially heated radiators.
• No heating or hot water.
• Gurgling or banging noises.
• Boiler repeatedly losing pressure.

These symptoms all point towards poor water circulation caused by low pressure.

How to Fix a Glow-worm F22 Fault

Only carry out checks you are comfortable doing safely. Internal boiler repairs should always be left to a Gas Safe registered engineer.

Check the pressure gauge

If the pressure is below the recommended level, use the filling loop to increase it to the manufacturer's recommended pressure.

Look for visible leaks

Check around the boiler, radiator valves and exposed pipework for signs of water escaping.

Reset the boiler

After restoring the pressure, reset the boiler. If the F22 code clears and does not return, the issue may have been temporary.

If the fault comes back or the pressure continues dropping, stop topping the system up repeatedly. A hidden leak or failed component is the more likely cause and should be diagnosed professionally.

When to Call a Gas Safe Engineer

Call an engineer if:

• the F22 fault keeps returning
• pressure drops again after topping up
• you find a leak
• you're unsure how to repressurise the boiler safely

A recurring F22 fault nearly always points to an underlying issue rather than normal pressure loss. If the pressure keeps dropping or the F22 fault returns, arranging a professional boiler repair in London is the safest way to identify and fix the underlying cause.

Frequently Asked Questions - (FAQs)

Use the filling loop underneath the boiler, opening the valves slowly while watching the gauge, and close them once the pressure reaches your model's recommended level — usually around 1.0 to 1.5 bar.

No — the boiler locks out deliberately when it detects low pressure, as a safety measure. Restore the pressure and reset the boiler before using it again.

Need Help With a Glow-worm F22 Fault?

If topping up the pressure doesn't solve the problem or the fault keeps returning, our Gas Safe engineers can diagnose the cause and carry out the necessary repairs.

Contact Serviceteam to book a boiler repair in London.