Heating & hot water
Boiler error codes, decoded
That flashing code is not a countdown to a bill. It is the boiler explaining what hurts in the only language it has, and nearly every code on every brand belongs to one of five families. Two of those families you can usually fix yourself before the kettle boils.
By the Tickover team · Published 9 February 2026 · 5 min read
How urgent is this?
Decode first. Panic never
A lockout is self-protection: the boiler has spotted a reading it does not like and stopped to keep itself, and you, safe. Most codes clear for good once the underlying cause is fixed.
What an error code actually is
Modern boilers watch themselves constantly: flame present, fan spinning, water pressure, temperatures at half a dozen points. When a reading strays out of range, the boiler performs a controlled stop and reports a code on the display. The full list lives in your manual and on the manufacturer’s website, and the same fault wears a different name on every brand: a low-pressure code on a Worcester Bosch looks nothing like the same complaint on a Vaillant, Ideal or Baxi.
Older or simpler boilers may have no screen at all, only a status light. The blink pattern is the code, and the manual decodes it the same way.
That is why the family matters more than the exact characters. Once you know which of the five stories the code is telling, you know whether the next move is yours or an engineer’s.
| Family | Usual culprit | Whose job |
|---|---|---|
| Low pressure | Recent bleeding or a slow leak | Yours: top up the system |
| Ignition or flame | Gas supply or ignition parts | Reset once, then engineer |
| Frozen condensate | Outside pipe iced overnight | Yours: thaw with warm water |
| Fan or flue | Worn fan, blocked flue | Engineer, without delay |
| Sensor or overheat | Tired sensor, pump or sludge | Engineer, quote the code |
The two families you can fix
A low-pressure code means the gauge has dipped below about 1 bar, and the fix is five minutes at the filling loop. A condensate code arrives on freezing mornings with a gurgling soundtrack, and warm water along the reachable outside pipe clears it. Everything else on the list is a visit.
The three families you cannot
Ignition lockouts happen when the burner tries to light and fails. Before booking, check the other gas appliances: if the hob is dead too, the problem is supply rather than boiler, and a prepayment meter out of credit has explained more than one urgent heating fault.
Fan and flue codes get less patience because the fan is what proves combustion gases are being pushed safely out of the house. The boiler refuses to run without that proof, and it is right to. Reset once at most; if the code returns, leave it locked out and book.
Overheat and sensor codes often trace back to circulation: a tired pump, a sticking valve, or sludge slowing the flow until temperatures spike. These are engineer visits too, though mentioning any cold-bottomed radiators when you book will point the diagnosis in the right direction.
Reset etiquette
The reset button exists because some lockouts are one-off events: a pressure blip, a gust down the flue, a brief interruption at the meter. One reset after checking the obvious is diagnosis. Ten resets is denial, and every extra attempt makes the boiler relight against whatever is actually wrong.
The safe reset sequence
Photograph the code before you do anything
Codes vanish when cleared. The photo turns your booking call from a vague symptom into a named fault.
Check the pressure gauge
Below 1 bar, top up first. Low pressure is the most ordinary lockout there is.
Glance at the weather
Freezing night plus gurgling boiler: thaw the condensate pipe before spending the reset.
Press reset once, as the manual shows
It is a front-panel button or dial position. Nothing behind the casing is ever part of the ritual.
Listen to the outcome
A clean restart earns a day of observation. The same code again means stop, book it in, and quote the code.
Living with codes
Do
- Keep the manual findable, or search your model number
- Note every code with a date, even ones that clear
- Give the code to the engineer when you book
- Check pressure and the condensate pipe before any reset
Don’t
- Do not reset repeatedly to outrun a recurring code
- Do not open the casing to investigate, ever
- Do not assume one code means the boiler is finished
- Do not ignore a code that returns every few days
Recurring codes have memories attached. A boiler that throws the same fan code every few weeks is announcing a part on its way out, and the cheap moment to act is before it fails outright. Mention the history at the annual service: patterns are half the diagnosis. For the wider map of symptoms beyond the display, from noises to cold radiators, there is the complete boiler guide.
Got a code on the screen right now?
Tell Self-Diagnose what the boiler is showing and doing. It will place the code family, rate the urgency, and set out what a vetted Gas Safe registered engineer will need to know.
Quick answers
Are boiler error codes the same on every brand?
No. Each manufacturer uses its own codes, so the same underlying fault wears different labels on a Worcester Bosch, Vaillant, Ideal or Baxi. The five fault families are universal though: pressure, ignition, condensate, fan and flue, and sensors. Find your exact code in the manual or on the manufacturer’s site, then think in families.
How many times can I safely reset my boiler?
Once, after checking the pressure gauge and, in winter, the condensate pipe. If the code returns, stop and book a Gas Safe registered engineer. Repeated resets force the boiler to relight against a live fault, which can turn a cheap repair into an expensive one.
Why does my boiler only show a code on cold mornings?
That pattern is the frozen condensate signature: overnight ice blocks the drain pipe, the boiler locks out at breakfast, and the fault sometimes clears itself as the day warms up. Thaw the reachable outside pipe with warm water, reset once, then lag the pipe so the sequel never gets made.
Does a lockout damage the boiler?
No. A lockout is the boiler declining to run until something is fixed, and it can sit that way indefinitely without harm. In freezing weather, though, a long shutdown raises the risk of frozen pipes elsewhere in the house, so treat a winter lockout with more urgency than a summer one.
This guide is general information for UK homes, not advice about your specific property. Anything involving gas must be done by a Gas Safe registered engineer, and notifiable electrical work by a qualified electrician. If you smell gas, call the National Gas Emergency line on 0800 111 999. If you’re ever unsure, stop and get a professional in — that’s exactly what Tickover is for.
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