Boiler Fault Codes Explained
What the error code on your boiler display means — the common Vaillant, Worcester Bosch, Ideal, Baxi and Glow-worm codes, which you can safely reset, and which need a Gas Safe engineer. Call 07927 882561.
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Upfront cost — no obligation Modern boilers show a fault or error code on the display when something stops them running safely. The code is a useful starting point — it points to the area of the problem — but it is not the full diagnosis: the same code can have several causes, and a Gas Safe registered engineer confirms the actual fault before repairing it. This guide explains the most common codes on the brands we work with across East London, which ones you can often clear yourself, and which mean it is time to call us on 07927 882561.
What a boiler fault code actually tells you
When a boiler locks out it shows a code — an F, E, L or EA number depending on the make — to flag which system has a problem: ignition, water pressure, the fan, a sensor, or overheating. A code narrows things down, but it does not tell you the root cause on its own. For example, a single ignition or flame code can be down to a faulty electrode, a gas supply issue, or a frozen condensate pipe in winter — very different repairs. Two codes are usually safe for a homeowner to deal with: low water pressure (top the system back up via the filling loop) and, in cold weather, a frozen condensate pipe (thaw the external pipe and reset). Anything involving ignition, flame loss, the fan or overheating should be diagnosed by a Gas Safe engineer — see our boiler repair page.
When a boiler locks out it shows a code — an F, E, L or EA number depending on the make — to flag which system has a problem: ignition, water pressure…
Vaillant and Glow-worm fault codes
Vaillant and Glow-worm are part of the same group and share a similar F-code system. F22 (Vaillant) / F1 & F22 (Glow-worm) mean low water pressure — usually fixable yourself by repressurising to around 1–1.5 bar with the heating cold. F28 is an ignition failure — the burner has tried to light and no flame was detected; in winter this is very often a frozen condensate pipe, otherwise it needs an engineer (see our Vaillant F28 fault guide). F29 is flame loss during operation. F75 is a pressure-sensor or pump fault, often caused by sludge from a system that has not been serviced or cleaned — our Vaillant F75 fault guide explains it, and a power flush is often part of the fix. We repair the full range as Vaillant and Glow-worm engineers.
Vaillant and Glow-worm are part of the same group and share a similar F-code system.
Worcester Bosch, Ideal and Baxi fault codes
Worcester Bosch: EA 227 means no flame detected — the most common Worcester code, and in cold weather almost always a frozen condensate pipe; otherwise it points to the ignition electrode or gas supply. C6 is a fan-speed fault and E9 is overheating — both need an engineer. If your Worcester has locked out, see our Worcester Bosch reset guide. Ideal Logic: F1 is low water pressure (usually a DIY refill), L1 is a low-flow or flow-temperature issue, L2 is an ignition lockout (low gas pressure, a blocked flue or faulty ignition), and F2 is flame loss — L2 and F2 need a Gas Safe engineer. We fix these as Ideal engineers. Baxi: E119 is low pressure (repressurise via the filling loop), E110 is an overheat, and E133 covers a gas-supply problem, ignition failure or a frozen condensate pipe. See our Baxi repair page. A recurring theme across every brand in winter is the frozen condensate pipe.
Worcester Bosch: EA 227 means no flame detected — the most common Worcester code, and in cold weather almost always a frozen condensate pipe; otherwise it…
What to do when a code appears — and when to call us
If the code is a pressure code, check the gauge and top up via the filling loop to around 1–1.5 bar (see low boiler pressure). If it is an ignition/flame code in cold weather, check whether the external condensate pipe has frozen and thaw it with warm water. Otherwise, reset the boiler once as the manufacturer instructs — but if it locks out again, stop: repeatedly resetting a boiler that keeps failing on ignition, flame, fan or overheat can be unsafe and rarely fixes anything. That is the point to call a Gas Safe registered engineer. Gas First (Gas Safe 587401) diagnoses the actual fault behind the code and gives you a clear price before any repair — we cover all of East London from our Bow and Dagenham bases, and can attend fast for a boiler that has stopped (boiler not turning on).
If the code is a pressure code, check the gauge and top up via the filling loop to around 1–1.5 bar (see low boiler pressure).
Frequently Asked Questions
Can I reset my boiler myself when it shows a fault code?
Usually yes, once — most manufacturers allow a single reset. But if the boiler locks out again on the same code, stop and call a Gas Safe engineer rather than resetting repeatedly.
Which fault codes can I fix myself?
Low water pressure codes (repressurise via the filling loop) and, in cold weather, a frozen condensate pipe (thaw the external pipe) are the two most homeowners can safely resolve.
Why does the same fault code keep coming back?
A code flags the area, not the root cause. If it returns, the underlying fault — ignition, a sensor, sludge, the fan — hasn't been fixed and needs diagnosing by an engineer.
Is it dangerous to keep running a boiler showing a fault code?
The boiler locks out to keep you safe, so it usually won't run. Don't override or repeatedly reset ignition, flame, fan or overheat codes — have them diagnosed.
Do all boilers show fault codes?
Most modern condensing boilers display a code. Older boilers may just lock out or show a light. Either way, we can diagnose the fault.
My boiler shows an ignition or flame code — what does it mean?
The burner has failed to light or the flame has been lost. In winter it's often a frozen condensate pipe; otherwise it typically needs an engineer to check the electrode, gas supply or gas valve.
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