Every defect on an EICR must be classified as C1, C2, C3, or FI. The code you choose determines whether the report is Satisfactory or Unsatisfactory — and whether the landlord faces a £40,000 penalty. This guide explains each code with real examples, common mistakes, and how Elec-Mate's Defect Code AI gets the right answer every time.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
The short answer
C1 means danger is present and a risk of injury exists right now. C2 means potentially dangerous — a risk of injury could arise. C3 means improvement recommended — non-compliant with the current standard but not dangerous. FI means further investigation is needed. Any C1 or C2 makes the report Unsatisfactory; C3 and FI are advisory under A4:2026.
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01 · Classification Guide
EICR observation codes are the classification system used to categorise defects, deficiencies, and departures from BS 7671 found during a periodic inspection and testing of an electrical installation. Every issue identified during the inspection is recorded in the observations table of the Electrical Installation Condition Report and assigned one of four classification codes.
The codes are defined in BS 7671:2018+A4:2026 and are explained in detail in IET Guidance Note 3: Inspection and Testing (GN3), which is the normative reference for code definitions. GN3 Table 3.5 sets out the explanation of C1, C2, C3, and FI and shall be consulted for code assignment (GN3). Note also that GN3 recognises a fifth outcome — an unlabelled "observation" — for items that do not require a code at all; this is distinct from C3, which does require an improvement to be recommended. The codes serve a critical purpose: they communicate the severity of each defect to the person responsible for the installation (the client, landlord, or building owner) and determine the overall assessment of the installation — Satisfactory or Unsatisfactory.
Getting the codes right matters. Under-classifying a dangerous defect as C3 instead of C2 could leave occupants at risk. Over-classifying a non-dangerous departure as C2 creates unnecessary alarm and undermines the credibility of the report. The four codes are:
| Code | Meaning | Action required | Overall assessment |
|---|---|---|---|
| C1 | Danger present — risk of injury exists now | Immediate action; make safe before leaving site | Unsatisfactory |
| C2 | Potentially dangerous — risk of injury could arise | Urgent remedial action | Unsatisfactory |
| C3 | Improvement recommended — non-compliant but not dangerous | Advisory; remediation optional | Satisfactory |
| FI | Further investigation — could not be fully assessed | Investigate without delay | Unsatisfactory |
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02 · Classification Guide
Risk of injury. Immediate remedial action required.
A C1 code means there is an immediate risk of injury from the defect. The danger exists right now — not under some future fault condition, but at the time of the inspection. The inspector must take immediate action to mitigate the danger before leaving site. This could mean isolating a circuit, disconnecting dangerous equipment, or making emergency temporary repairs. The person responsible for the installation must be advised to take immediate action.
Exposed live conductors accessible to occupants — for example, a damaged socket faceplate with live terminals visible, or a junction box with a missing cover in an accessible location.
Absence of earthing on exposed metalwork that is live — for example, a metal light fitting with no earth connection where the live conductor has come into contact with the metalwork.
A consumer unit with the cover removed or damaged, exposing live busbars that could be touched.
An electric shower with a broken connection that has resulted in the metalwork of the shower unit becoming live.
A cable that has been damaged by rodents or mechanical impact, with live conductors exposed and accessible.
C1 defects are relatively rare in practice. Most inspectors encounter them infrequently because truly dangerous conditions tend to be obvious even before formal testing. However, when they are found, they must be addressed immediately and cannot be left for the client to deal with later.
03 · Classification Guide
Risk of injury may arise. Urgent remedial action required.
A C2 code means there is no immediate danger at the time of inspection, but a risk of injury could arise under reasonably foreseeable conditions. The defect is serious enough that it requires urgent remedial action — it cannot simply be noted and left. C2 is the most common classification for significant defects found during periodic inspections, and it is the code that causes the most debate between electricians.
Absence of RCD protection on socket outlet circuits where required by BS 7671 — particularly in bathrooms, kitchens, and circuits supplying equipment intended for outdoor use.
Missing circuit protective conductor (CPC / earth wire) connection at an accessory — the socket or light fitting has no earth, meaning metalwork could become live under a fault condition.
Earth fault loop impedance (Zs) exceeding the maximum permitted value for the protective device — meaning the device may not disconnect within the required time during a fault.
Absence of main protective bonding to gas, water, or oil services as required by Regulation 411.3.1.2 — extraneous-conductive-parts liable to introduce a dangerous potential difference shall be connected to the main earthing terminal.
A circuit breaker or fuse that is incorrectly rated for the cable it protects — for example, a 32A MCB protecting a 1.0mm squared cable.
Mixed wiring colours (old red/black with new brown/blue) without a warning notice at the distribution board — Regulation 514.14 was deleted in BS 7671:2018+A4:2026, but OSG (9th Ed) still recommends affixing a notice where mixed colours exist, and the absence of such a notice creates a risk of incorrect identification during future work.
An RCD that fails to trip within the required time during testing.
Lack of adequate overcurrent protection — for example, a rewirable fuse that has been replaced with incorrectly rated fuse wire.
C2 is the code that generates the most remedial work. For landlord EICRs, any C2 observation makes the report Unsatisfactory and triggers the 28-day remedial deadline. For electricians, this is where the remedial quoting opportunity lies.
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Not sure if it is C2 or C3? Type or dictate the defect in plain English and Elec-Mate's AI returns the correct classification code with the matching BS…
04 · Classification Guide
Does not comply with current standard but not dangerous.
A C3 code means the installation does not comply with the current edition of BS 7671 but the non-compliance is not dangerous and does not pose a foreseeable risk of injury. C3 items are advisory — they represent improvements that would be required if the installation were being designed and installed today, but were acceptable under the regulations in force when the original work was carried out. C3 observations do not affect the overall assessment of the EICR. A report with no C1 or C2 observations (only C3 and/or FI, or none) is classified as Satisfactory.
Absence of surge protection device (SPD) — required for new installations under BS 7671 Regulation 443.4 but not dangerous if absent in an existing installation.
Older wiring colours (red/black) throughout the installation where no mixing with new colours has occurred — not dangerous but noted as a departure from the current harmonised colour scheme.
Absence of supplementary bonding in a bathroom where the conditions of Regulation 701.415.2 are met (all circuits RCD protected, main bonding effective) — no longer required by current regulations.
Lack of cable support clips at the intervals specified in the current edition — typically seen in older installations where the cable is securely fixed but not at the precise intervals required today.
Absence of IP-rated accessories in a location where the current edition would require them, but the existing accessories are in serviceable condition and the location does not present an immediate hazard.
Absence of arc fault detection devices (AFDDs) — under Regulation 421.1.7 (BS 7671:2018+A4:2026), AFDDs conforming to BS EN 62606 "shall be provided" for single-phase AC final circuits supplying socket-outlets rated up to 32 A in high rise residential buildings (HRRBs), houses in multiple occupation (HMOs), purpose-built student accommodation and care homes. For all other premises the same regulation only "recommends" them. In ordinary domestic premises (which fall outside the mandatory categories) the absence of AFDDs is therefore typically recorded as C3; in the four named building types it carries more weight and the classification should reflect the foreseeable fire risk.
While C3 items are not mandatory to fix, they should be communicated to the client clearly. Many clients choose to address C3 items during the remedial visit for C2 defects, as the electrician is already on site and the incremental cost is low. From a professional standpoint, recording C3 items demonstrates thoroughness and helps the client understand what would need to be addressed if the installation were to be brought fully up to the current standard.
05 · Classification Guide
Could not be fully assessed. Investigation needed without delay.
FI is different from the other three codes. It does not classify the severity of a known defect — it indicates that the inspector could not fully assess a part of the installation. The reason may be restricted access, unexpected test results that need deeper analysis, or concealed wiring that shows signs of deterioration but cannot be fully examined without more intrusive investigation. FI means "we do not know the full picture yet" and further work is required to determine whether the issue is C1, C2, C3, or actually acceptable.
Insulation resistance readings that are low but not definitive — for example, a reading of 1.5 megohms on a circuit where 200+ megohms would be expected. The cable may be deteriorating but cannot be fully assessed without lifting floorboards or opening up walls.
A circuit that could not be tested because equipment could not be disconnected — for example, a dedicated circuit supplying a burglar alarm or medical equipment where the client would not permit disconnection.
Signs of overheating at a connection that could not be fully accessed — for example, discolouration visible through a gap in a ceiling void that requires removal of the ceiling to investigate fully.
An earth electrode on a TT system where the resistance is borderline and the electrode cannot be accessed for further testing without excavation.
A consumer unit or distribution board in a locked room or behind fixed furniture that could not be accessed during the inspection.
FI observations must be actioned "without delay." The client or landlord should arrange for the further investigation to take place as soon as practicable. Once the investigation is complete, the FI code is replaced with the appropriate classification (C1, C2, C3, or removed entirely if no defect is found). For landlord EICRs, FI observations should be treated with urgency — a local authority may consider an unresolved FI as evidence that the landlord has not met their obligations.
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06 · Classification Guide
The overall assessment on an EICR is determined entirely by the observation codes present in the report. The rules are straightforward:
Elec-Mate tracks observation codes as you add them to the EICR. If any C1 or C2 is recorded, the report cannot be issued as Satisfactory until the overall assessment is set to Unsatisfactory. That stops a report going out Satisfactory with a C2 on it, one of the most common mistakes flagged by scheme provider audits.
FI is used where the inspector could not fully determine the condition of part of the installation within the agreed limits. Before A4:2026 an FI had to be marked unsatisfactory; the A4:2026 model EICR now treats C3 and FI as advisory, so they do not affect the overall assessment. The investigation should still be carried out promptly so the item can be properly classified. The authority for the codes themselves is GN3, which states that one of the four codes (C1, C2, C3, or FI) shall be allocated to each observation to indicate the degree of urgency for remedial action — and GN3 directs inspectors to GN3 Table 3.5 for the detailed explanation of each code.
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Elec-Mate watches your observation codes as you work. A report with a C1 or C2 on it cannot be issued as Satisfactory.
07 · Classification Guide
Getting observation codes wrong is one of the most common reasons for EICR reports being rejected or queried by competent person scheme providers. The table below summarises how the most commonly debated defects are usually classified, and the single factor that decides between codes. Classification always depends on the full picture on site — these are the typical positions, not absolute rules.
| Defect | Typical code | Deciding factor |
|---|---|---|
| No RCD protection on socket circuit in a domestic property | C2 | Foreseeable shock risk; difficult to justify C3 for any domestic socket circuit |
| No RCD on a domestic luminaire (lighting) final circuit | C2 | Reg 411.3.4 (since 2018) makes 30 mA RCD mandatory for new work; foreseeable risk on existing circuits |
| Missing main protective bonding to a service | C2 | Reg 411.3.1.2; metalwork could become live under fault. C1 only if already at a dangerous potential |
| No supplementary bonding in a bathroom | C3 / none | May be omitted where Reg 701.415.2 conditions (ADS, 30 mA RCD, effective main bonding) are all met |
| Absence of a surge protection device (SPD) | C3 | Required for new work under Reg 443.4; not dangerous if absent in an existing installation |
| Absence of AFDDs in ordinary domestic premises | C3 | Reg 421.1.7 only recommends AFDDs outside HRRBs, HMOs, student accommodation and care homes |
Here are the mistakes inspectors make most often:
The absence of RCD protection on socket circuits in wet areas (bathrooms, kitchens near sinks) is a C2 defect, not C3. While the circuit may have been compliant when originally installed, the risk of electric shock in wet environments is a foreseeable danger that warrants urgent remedial action. C3 would only apply where the absence of RCD protection creates no foreseeable risk of injury — which is difficult to justify for any socket circuit in a domestic property.
This is a hard rule with no exceptions. Any C1 or C2 observation makes the overall assessment Unsatisfactory. Some electricians mark a report Satisfactory despite a C2 being present because the client pressures them or because the defect seems minor. This is incorrect and will be flagged by scheme provider audits. It can result in disciplinary action and, in a landlord context, could leave the landlord unknowingly non-compliant with the 2020 Regulations.
Writing "no bonding" or "RCD fail" is not sufficient. The observation must include enough detail that a different electrician could find and rectify the issue: what is missing, where it is located, and (ideally) the relevant BS 7671 regulation reference. For example: "Absence of main protective bonding to incoming gas supply at meter position — Regulation 411.3.1.2" is far more useful than "no bonding."
FI should only be used when you genuinely could not fully assess the issue. It is not a catch-all for "I am not sure what code to use." If you can see the defect, can identify the problem, and have enough information to classify it, it should be classified as C1, C2, or C3 — not FI. Over-use of FI is a red flag in scheme provider audits and suggests the inspector may not have the competence or confidence to make classification decisions.
Some inspectors skip C3 items because they do not affect the overall assessment. This is poor practice. Recording C3 items demonstrates thoroughness, provides the client with a complete picture of their installation, and creates a record for future inspections. It also generates additional remedial work opportunities — many clients choose to address C3 items alongside C2 remedials.
08 · Classification Guide
The hardest part of completing an EICR is not the testing — it is deciding what code to assign. Is missing bonding in the bathroom C2 or C3? Is a Zs reading that is 5% over the maximum a C2 or just a marginal pass? Is the absence of an SPD a C3 or should it not be recorded at all?
Elec-Mate solves this with the Defect Code AI — one of the 8 Elec-AI agents built into the app. Here is how it works:
Type or dictate: "No RCD protection on socket circuit in bathroom" or "Missing earth connection on metal light fitting in upstairs landing" or "Zs reading of 1.92 ohms on a B32 radial circuit."
The AI analyses your description against BS 7671:2018+A4:2026 and IET Guidance Note 3. It returns the recommended code (C1, C2, C3, or FI), the specific BS 7671 regulation reference, and an explanation of why that code applies.
You always have the final say. If you agree with the AI classification, tap to add it to the EICR. If you disagree, override it with your professional judgement. The AI provides a starting point — you make the decision.
The Defect Code AI eliminates the most time-consuming and stressful part of EICR completion. Instead of flicking through GN3 trying to decide between C2 and C3, you get a regulation-backed answer in seconds. Combine it with the AI board scanner, voice test entry, and the remedial works estimator, and you have a complete EICR workflow that runs from arrival on site to sending the finished certificate — all from your phone.
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Describe any defect in plain English and get the correct EICR classification code with the matching BS 7671 regulation.
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