Can I top up boiler pressure myself?

Yes — most modern boilers have an external filling loop or built-in filling key. Open the valves slowly to bring pressure to 1.0–1.5 bar (cold), then close. If you have to do this more than once a month, you have a leak — call us to find it before something fails.

What does it mean if the code clears but comes back?

The fault is intermittent or the underlying cause hasn't been fixed. Common examples: a flame-sense electrode that fires fine when warm but fails when cold, a pressure sensor that reads correctly until heat-cycle expansion shifts it. Need engineer diagnosis with a fault-code reader.

Is a fault code on a 15-year-old boiler a sign to replace?

Often, yes — see our guide on signs you need a new boiler. On boilers over 12 years old, a single major repair quote usually means replacement is the better economic choice.

Will my boiler manufacturer warranty cover the repair?

Yes if (a) the boiler is within warranty (typically 7–10 years from install), (b) it's been annually serviced by a Gas Safe engineer with records kept, and (c) the failure isn't caused by something excluded (sludge, scale, freezing). Always check before paying.

How much does a typical boiler repair cost?

Every repair is quoted as a fixed price before any parts are ordered — common parts that fail (pressure sensor, fan, ignition lead, diverter valve) sit at the lower end, larger items (PCB, gas valve, pump) in a higher band, and heat exchanger replacements highest. Diagnostic visits are a fixed-price call-out if no parts are needed.

Do you stock parts for all major brands?

We stock the most common failure parts on the van for Worcester Bosch, Vaillant, Ideal, Baxi and Glow-worm. Less common parts are usually next-day from the merchant. Most NN17/NN18 callouts are back on within the same visit.

Guide · Boiler Repair

Common Boiler Fault Codes Explained

Most modern boilers display a fault code rather than just locking out — and most codes point to the same handful of failure modes across all brands. Here's how to translate what your boiler is telling you.

6 min readBy Carl Eddershaw, Director & Lead EngineerLast updated May 2026

Quick answer

The most common fault codes in 2026 are pressure loss (Worcester EA, Vaillant F22, Ideal F1, Baxi E118), ignition failure (Worcester EA/CE, Vaillant F28/F29, Ideal L2, Baxi E133), and pump or sensor faults (Vaillant F75, Worcester E9). Pressure loss is usually a simple top-up; ignition failures are nearly always gas-supply or PCB issues; F75/E9 codes mean a Gas Safe call-out — don't keep resetting.

Worcester Bosch fault codes you'll actually see

EA — Flame not detected after ignition. 80% of EA codes we see are a failed flame-sense electrode or a dirty burner. The other 20% are a failed gas valve. PCB-related EA codes are rare but happen on older Greenstars.
CE 207 — Low pressure. Top up the system to 1.0–1.5 bar via the filling loop. If pressure drops again within a week, you have a leak — call us.
D5 — Low pressure during heating cycle. Same root cause as CE 207 most often, but can also indicate a failed expansion vessel (cheap fix) or failed PRV (also cheap).
E9 / E168 — Overheat or PCB lockout. Don't keep resetting — these usually point to pump failure, blocked heat exchanger or PCB issue. Gas Safe engineer needed.
H07 — Low pressure warning (informational). Top up; same as CE 207 if it persists.

Vaillant fault codes

F22 — Low water pressure. Top up to 1.0–1.5 bar via the filling key. Recurring F22 = leak, internal or external.
F28 — No gas / failed ignition. Check gas is on (smart meter prepayment? other appliances working?), then call out — flame sense or gas valve fault.
F29 — Flame loss during operation. Similar root causes to F28; sometimes flue blockage or condensate trap full of water.
F75 — Pump fault / no pressure rise after pump start. Often a stuck pressure sensor (cheap fix from van stock) or a seized pump (more involved).
F1 (oil ecoTEC) — Low oil pressure. Check oil level in tank first; if oil is fine, fire valve or filter likely blocked.

Ideal and Baxi fault codes

Ideal L2 — Ignition lockout (Logic, Vogue, Atlantic). Same family as Worcester EA — flame sense or gas valve in 80% of cases.
Ideal F1 — Low pressure (Logic, Independent). Top up to 1–1.5 bar.
Ideal F2 — No flame signal. Same as L2 family — gas supply or sense electrode.
Baxi E118 — Low pressure. Top up via filling loop. Recurring = leak.
Baxi E133 — Ignition fault / no flame. Similar fault tree to Worcester EA.
Baxi E168 — Generic boiler fault, often PCB-related. Call out.

Fault code translation across major brands

Brand-specific code tables are deeper than this — these are the codes we see most often on call-outs across Northamptonshire and Rutland in 2026. Always cross-reference with your boiler's manual before assuming a diagnosis.

Issue	Worcester	Vaillant	Ideal	Baxi
Low pressure	CE 207 / H07	F22	F1	E118
Ignition failure	EA	F28	L2 / F2	E133
Flame loss running	EA (post-light)	F29	L2	E133
Pump / sensor	E9	F75	F4 / F9	E160 family
Overheat	E168	F20	F3	E110
Fan fault	E168 family	F32	F6	E125

When to stop and call us

You've reset the boiler more than twice and the same code returns within a day
The code involves the gas valve, PCB, fan, pump, or heat exchanger
You smell gas, see soot around the flue, or have a yellow flame
Pressure drops consistently after top-up — there's a leak that needs finding
The boiler is locked out and the manual reset doesn't restore operation

Most of the parts that fail on Worcester, Vaillant and Ideal boilers we carry on the van — pressure sensors, fans, ignition leads, gas valves, diverter valves and pumps. Most call-outs across our daily-run area are back-on within the same visit. See our same-day boiler repair service for what's included.

Never bypass a fault code by repeatedly resetting — modern boilers lock out for safety reasons. If the code keeps returning, the underlying problem is still there and could escalate to a more expensive failure or, in the case of combustion faults, a CO risk.

About the author

Carl Eddershaw

Director & Lead Engineer · Reactive Gas Heating & Plumbing

Reactive runs from its workshop at Rutherford Court in Corby. Gas Safe registered, OFTEC registered for oil and certified for LPG, with daily on-the-tools experience installing, repairing and servicing boilers across Northamptonshire, Rutland and Leicestershire. Every guide on this site is written from real call-out notes — not generic copy.

Frequently asked questions

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Boiler showing a fault code? Get it diagnosed today.

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See the full boiler repair service: see same-day boiler repair · book a fixed-price diagnostic · boiler repair in Corby & Northants

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Last updated May 2026

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