How We Source Fault Codes

Last reviewed 27 April 2026

Every fault code on this site is sourced from official manufacturer documentation. We do not source fault codes from forum threads, community wikis, or other third-party sites. This page describes exactly how we do it.

The data — by the numbers

33,565 fault codes
750 boiler models
29 UK manufacturers covered
500+ manufacturer service / installation manuals held in our archive

Step 1 — Acquire the source manual

For each boiler model we cover, we obtain the official manufacturer service manual or installation/user guide. Sources include:

Manufacturer documentation portals (Worcester Bosch, Vaillant, Ideal, Baxi, Glow-worm, etc.)
Trade-supplier manual archives
Manufacturer-distributed reference packs for engineers

Step 2 — Extract the codes

Fault codes are extracted from each manual. Where the manual is machine-readable PDF, we extract the text directly. Where it is a scanned image, we use OCR (optical character recognition) and then manually verify the result against the visual scan.

Each extracted code captures the manufacturer's own technical description verbatim — that becomes the "Technical description" blockquote you see on every fault code page.

Step 3 — Plain-English rewrite

Manufacturer descriptions are written for engineers. We rewrite each one in plain English for homeowners — without changing the underlying technical meaning. Where the original says "PCB has detected a flame signal in the absence of a demand for ignition", the plain English summary becomes "the boiler thinks the burner is on when it shouldn't be".

Step 4 — Severity, DIY-safe and cost

For every code we additionally assess:

Severity — Emergency / High / Medium / Low — based on safety implication and impact on heating/hot water.
DIY-safe — only flagged when the resolution involves no gas, no electrics, no sealed components, and no flue work. Conservatively assigned.
Repair cost — estimated from current UK trade rates (parts + labour). Reviewed annually.
Common parts replaced — drawn from the manufacturer's diagnostic flowchart or service bulletin where available.
Cause description — short root-cause note in plain English.
Seasonal note — added where the fault has a strong seasonal pattern (e.g. frozen condensate pipes in winter).

Step 5 — Inherited series codes

Where a specific model has no available service manual but is part of a documented product series (for example, a Vaillant ecoTEC plus 825 that shares the ecoTEC plus fault code set), we inherit the fault code data from the parent series.

Inherited codes are flagged internally with a source_inherited_from field. We only inherit codes within the same product family from the same manufacturer, where the fault-handling system is documented as shared.

Step 6 — Validation

Before publication, every code passes through automated validation checks for:

Code format consistency
Severity / DIY-safe contradictions (e.g. an "Emergency" code can never be DIY-safe)
Cost realism (no £0 fixes flagged as engineer-required)
Cross-references to related codes that exist in the database
Source-manual provenance

Codes that fail validation are held for manual review and are not published until resolved.

Manufacturers covered

We currently hold and source from the official documentation of:

Spotted an issue?

If a fault code on this site doesn't match what you see in the manufacturer's manual or what your engineer has told you, please email hello@boilerfaultcodes.com with the page URL. We'll re-verify against our source manual and correct the record where appropriate.