Quick Answer
Boiler fault codes are letters or numbers your boiler’s display shows to explain why it has stopped working, and the exact meaning depends on the brand. F1 on an Ideal boiler means low water pressure, L2 on an Ideal means ignition lockout, and F22 on a Vaillant or Glow-worm also means low pressure. Always check your specific brand’s manual before acting, since the same code can mean different things on different makes.
Why Codes Differ Between Brands
Every boiler manufacturer designs its own control software and display system, so there is no single universal code list across the industry. Worcester Bosch, Vaillant, Ideal, and Baxi each use a different combination of letters and numbers for the same underlying faults, which is why the same code, F1 for example, points to different problems depending on which boiler you own.
F1 – What It Means and How to Fix It
On an Ideal boiler, F1 signals low water pressure. Check the pressure gauge, and if it reads below around 1 bar, top up the system using the filling loop until it sits between 1 and 1.5 bar. If the pressure keeps dropping again within days or weeks, this points to a leak or a faulty expansion vessel rather than a one-off issue, and is worth having checked by a Gas Safe registered engineer.
L2 – What It Means and How to Fix It
L2 on an Ideal boiler means ignition lockout, also called flame loss. The boiler has tried to ignite several times, failed, and shut itself down as a safety measure. Common causes include a frozen condensate pipe in cold weather, a gas supply issue, or a fault with internal ignition components. A simple reset sometimes clears a one-off lockout, but repeated L2 faults need a Gas Safe engineer to investigate the underlying cause.
F22 – What It Means and How to Fix It
F22 is Vaillant and Glow-worm’s version of a low pressure fault, functionally the same issue as Ideal’s F1. Check the pressure gauge and top up using the filling loop in the same way. As with any pressure-related code, if it recurs shortly after topping up, treat it as a sign of a leak rather than repeatedly refilling the system.
Common Codes Across Major UK Brands
| Brand | Low Pressure Code | Ignition Lockout Code |
|---|---|---|
| Ideal | F1 | L2 |
| Vaillant / Glow-worm | F22 | F28 |
| Baxi | E119 | E133 |
| Worcester Bosch | A1 | EA |
These are the most commonly searched codes for each brand, but manufacturers periodically update their code lists, so always cross-check against your specific model’s manual where possible.
When to Call an Engineer vs DIY Reset
- A single low pressure code that clears after topping up the system is generally safe to resolve yourself
- A code that returns within days or weeks of a top-up or reset needs a Gas Safe engineer, since this points to an underlying fault rather than a one-off issue
- Ignition lockout codes that persist after checking for a frozen condensate pipe or a lapsed prepayment meter should be looked at by an engineer
- Never attempt to open or work on the internal components of a boiler yourself, since only a Gas Safe registered engineer is legally permitted to do so
Related Reading
If your fault code points to a leak rather than a simple reset, see our guide on why your boiler might be leaking water. For Worcester Bosch owners specifically, see how to reset a Worcester Bosch boiler.
Frequently Asked Questions
Does F1 mean the same thing on every boiler brand?
No, F1 specifically refers to low pressure on Ideal boilers, while other brands use entirely different codes for the same fault.
Can I fix a low pressure fault code myself?
Often yes, by topping up the system pressure using the filling loop, though repeated low pressure needs an engineer to check for a leak.
Why does my boiler show an ignition lockout code in winter specifically?
A frozen condensate pipe is a common winter cause of ignition lockout codes, alongside gas supply or internal ignition issues.
Is it safe to keep resetting my boiler when a code appears?
Occasional resets are fine, but a code that keeps returning after resetting means the underlying issue has not been fixed and needs professional attention.
Where can I find my exact boiler’s fault code list?
Your boiler’s user manual, usually available as a PDF from the manufacturer’s website using your specific model number, gives the definitive code list for your unit.