--- title: "Common Boiler Fault Codes Explained | Reactive" description: "A Gas Safe engineer decodes the most common Worcester, Vaillant, Ideal and Baxi fault codes — what each means, what to try, and when to stop and call." lang: en-GB json-ld: | [ { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "Can I top up boiler pressure myself?", "acceptedAnswer": { "@type": "Answer", "text": "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." } }, { "@type": "Question", "name": "What does it mean if the code clears but comes back?", "acceptedAnswer": { "@type": "Answer", "text": "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." } }, { "@type": "Question", "name": "Is a fault code on a 15-year-old boiler a sign to replace?", "acceptedAnswer": { "@type": "Answer", "text": "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." } }, { "@type": "Question", "name": "Will my boiler manufacturer warranty cover the repair?", "acceptedAnswer": { "@type": "Answer", "text": "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." } }, { "@type": "Question", "name": "How much does a typical boiler repair cost?", "acceptedAnswer": { "@type": "Answer", "text": "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." } }, { "@type": "Question", "name": "Do you stock parts for all major brands?", "acceptedAnswer": { "@type": "Answer", "text": "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." } } ] }, { "@context": "https://schema.org", "@type": "Article", "@id": "https://reactiveplumbing.co.uk/guides/common-boiler-fault-codes-explained#article", "headline": "Common Boiler Fault Codes Explained", "description": "A Gas Safe engineer decodes the most common Worcester, Vaillant, Ideal and Baxi fault codes — what each means, what to try, and when to stop and call.", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://reactiveplumbing.co.uk/guides/common-boiler-fault-codes-explained" }, "author": { "@type": "Person", "name": "Carl Eddershaw", "jobTitle": "Director & Lead Engineer", "worksFor": { "@id": "https://reactiveplumbing.co.uk/#localbusiness" } }, "publisher": { "@id": "https://reactiveplumbing.co.uk/#organization" }, "datePublished": "2026-05-01", "dateModified": "2026-05-01", "image": "https://reactiveplumbing.co.uk/favicon.png", "inLanguage": "en-GB" }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://reactiveplumbing.co.uk" }, { "@type": "ListItem", "position": 2, "name": "Heating & Gas Services", "item": "https://reactiveplumbing.co.uk/heating-gas-services" }, { "@type": "ListItem", "position": 3, "name": "Boiler Repair", "item": "https://reactiveplumbing.co.uk/boiler-repair" }, { "@type": "ListItem", "position": 4, "name": "Common Boiler Fault Codes Explained", "item": "https://reactiveplumbing.co.uk/guides/common-boiler-fault-codes-explained" } ] }, { "@context": "https://schema.org", "@type": "Person", "name": "Carl Eddershaw", "jobTitle": "Director & Lead Engineer", "image": "https://reactiveplumbing.co.uk/favicon.png", "worksFor": { "@id": "https://reactiveplumbing.co.uk/#localbusiness" }, "knowsAbout": [ "Gas Safe boiler installation", "OFTEC oil heating", "LPG installations", "Plumbing & drainage" ] } ] --- Gas Safe Registered · OFTEC Registered · Checkatrade Verified 9 Rutherford Court, Corby NN17 4SJ [info@reactiveph.co.uk](mailto:info@reactiveph.co.uk) [![Reactive Gas Heating & Plumbing logo](/__l5e/assets-v1/51d713a4-18a4-4b5f-96fb-2fcce169e56c/reactive-logo.png)](/) ServicesAreasGuides[About](/about)[Our Work](/our-work)[Plans](/maintenance-plans)[Reviews](/reviews)[Contact](/contact) [24/7 Call 07915 906262 ](tel:+447915906262)[Fixed Boiler Quote](/boiler-quote) 1. [Home](/) 2. [Heating & Gas Services](/heating-gas-services) 3. [Boiler Repair](/boiler-repair) 4. Guide 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 read By Carl Eddershaw, Director & Lead Engineer Last 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](/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 ### Can I top up boiler pressure myself? ### What does it mean if the code clears but comes back? ### Is a fault code on a 15-year-old boiler a sign to replace? ### Will my boiler manufacturer warranty cover the repair? ### How much does a typical boiler repair cost? ### Do you stock parts for all major brands? Need a hand? ## Boiler showing a fault code? Get it diagnosed today. Same-day diagnostics on most makes from our Corby base, fixed-price repair quotes, and most parts on the van. Phone answered 24/7 for emergencies. 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