Glow-worm F22 fault code — what it means and how to fix it

What does the Glow-worm F22 fault code mean?

The Glow-worm F22 fault code means system water pressure has dropped too low and the boiler has shut down to protect itself. Repressurise to 1.0–1.5 bar via the filling loop and reset. If the pressure falls again or F22 keeps returning, there may be a leak or a faulty pressure sensor.

In plain terms: your boiler needs a certain amount of water pressure in the heating system to run safely. When that pressure drops below the minimum, the boiler stops rather than fire up with too little water — a bit of built-in self-protection. Topping the system back up usually clears it.

F22 shows up across Glow-worm's own ranges — the Energy, Betacom 4, Easicom, Ultracom and Flexicom models all use it. The wording and the reset button vary slightly between models, so it's always worth checking the code against your boiler's manual.

F22 is closely related to F9, the other Glow-worm pressure code. F22 is the low-pressure shutdown; F9 flags a pressure-sensing issue. For a homeowner the first checks and the fix are the same — top the pressure back up and see whether it holds.

Key facts

The quick version, before the detail.

• What it means: low system water pressure shutdown (dry-fire protection).
• DIY-fixable: yes — repressurise to 1.0–1.5 bar via the filling loop.
• Gas Safe job if: pressure keeps dropping (a leak), or the sensor or pump has failed.
• Related code: F9 (pressure-sensing fault).
• Smart Plan boiler cover: parts and labour are capped at £500 a year (boiler under 7 years) or £200 a year (7 years or older) — a larger repair can cost more than the cap, and you pay the difference.
• A £95 call-out fee can apply when an engineer visits; call-outs run Monday to Friday, 08:00–18:00.
• Using a service starts a 12-month agreement period — leave early and 75% of the remaining months is payable.

F22 and F9 at a glance

Why does the Glow-worm F22 code appear?

F22 fires when system pressure drops below the safe minimum, so the boiler stops to protect itself. A one-off drop over several months is normal — systems lose a little pressure naturally, and topping up sorts it. A fast repeat drop is different: it usually points to a leak.

There are four common causes:

Pressure below minimum. The system has slowly lost water over time and simply needs topping back up — the most common and most harmless cause.

A leak. Water escaping from a radiator, a pipe joint, a valve or the boiler itself will pull the pressure down again soon after you top it up.

A faulty low-water-pressure sensor. The pressure may be fine, but a failing sensor reads it as low and shuts the boiler down anyway.

A failed pump. If the pump can't move water round the system, the boiler's dry-fire protection can step in and trigger the fault.

How to fix the Glow-worm F22 code yourself

You can usually clear F22 yourself by repressurising the system — a genuine homeowner job that doesn't involve opening the boiler or touching anything to do with gas. Here's the order to do it in.

1. With the boiler cold, check the pressure gauge. On most Glow-worm models it should read between 1.0 and 1.5 bar when cold. If F22 is showing, it'll usually be sitting well below 1.

2. Find the filling loop — the braided silver hose beneath the boiler, with a valve (or two) at each end. Some are built in with a key; check your manual if you're not sure which it is.

3. Open both valves slowly. You'll hear water flowing and see the gauge start to climb. Keep going until it reads about 1.0–1.5 bar.

4. Close both valves fully, then press the reset button so the boiler restarts. It should now fire up and run normally.

Don't exceed about 1.5 bar — over-filling can trip the pressure-relief valve and leave you with the opposite problem. If the gauge won't hold, keeps falling after you top up, or F22 comes straight back, stop there and book a Gas Safe registered engineer. Repeatedly topping up masks the real cause and adds fresh oxygen to the water, which speeds up corrosion inside the system.

When to call a Gas Safe registered engineer for F22

Call an engineer if the pressure keeps dropping after you've topped it up, if F22 returns soon after a reset, or if you can see water anywhere near the boiler, pipework or radiators. A repeating F22 almost always means a leak somewhere in the system, and a stuck sensor or a failed pump both need qualified diagnosis and repair.

Tracing and fixing a leak, or replacing a pressure sensor or a pump, is a chargeable repair — what it costs depends on the fault, the parts and where you are, so get a quote before the work starts. You can check that any engineer you use is qualified on the Gas Safe Register.

If you'd rather spread the cost of repairs like these, Smart Plan's boiler module is one option — but read the limits first, because they decide whether you're actually covered. Smart Plan is a service plan, not insurance: you pay a regular amount whether or not you ever claim, and the cover is capped. A boiler module covers parts and labour up to £500 a year if your boiler is under 7 years old, or up to £200 a year if it's 7 years or older — so a bigger repair can cost more than the cap, and the balance is yours to pay. A £95 call-out fee can apply when an engineer is sent out, and call-outs run Monday to Friday, 08:00–18:00.

The term that catches people out: the moment you use a service, a 12-month agreement period begins. If you leave before it ends, 75% of the remaining months is payable — so it isn't a one-off fix, it's a commitment. Cover is modular, meaning you choose which modules to take, but you keep paying for each one you hold. The plan is provided by UK Boiler Company Ltd, trading since 2014.

One safety note: F22 itself is a pressure fault, not a gas emergency. But if you ever smell gas or your carbon monoxide alarm sounds, stop, open the windows, turn the gas off at the meter, don't touch electrical switches, leave the house, and call the National Gas Emergency Service on 0800 111 999.

Glow-worm F22 fault FAQs

Thinking about boiler cover?

Smart Plan's boiler module covers parts and labour up to your cover limit — £500 a year under 7 years, £200 a year for 7 years and older. It's a service plan, not insurance. Before you sign up, the terms that matter: a £95 call-out fee can apply, call-outs run Monday to Friday 08:00–18:00, a repair larger than your limit can leave you paying the difference, and using a service starts a 12-month agreement period (75% of the remaining months is payable if you leave early). If that works for you, you can build a plan below.

Helpful links

• All Glow-worm fault codes
• Boiler & central heating cover
• No heating? Book a repair
• Build your plan
• Glow-worm fault codes (official)
• Check an engineer on the Gas Safe Register