The short answer
An FI code on an EICR means "further investigation required without delay". It is used when the inspector finds something that could not be fully assessed during the inspection and needs deeper investigation to determine whether it is a genuine fault — and how serious. An FI is not a code for a defect that is understood; it flags an unresolved concern that warrants prompt follow-up. Because the safety of that item is unconfirmed, any FI makes the overall report unsatisfactory, just like C1 and C2. The next step is to carry out the further investigation, which may then confirm the installation is fine or reclassify the item as a C1, C2 or C3.
FI is the code people understand least, because it does not describe a known fault — it describes a question the inspection could not answer. The sections below explain when it is used and what follows.
FI essentials
- MeaningFurther investigation required
- TimeframeWithout delay
- Why usedConcern not fully assessed
- Effect on resultUnsatisfactory
- Next stepInvestigate, then reclassify
What 'further investigation' means
The codes C1, C2 and C3 are all applied to issues the inspector has identified and understood — they know what the fault is and how serious it is. FI is different. It is used when the inspection reveals a potential problem that cannot be resolved on the spot, so the inspector cannot yet say whether it is dangerous.
The model report wording is "Further investigation required without delay." In other words, the inspector has found a reason for concern but needs to investigate further — perhaps by opening up part of the installation, carrying out additional testing, or examining something that was not accessible during the standard inspection — before they can give it a proper classification.
It helps to think of the other codes as answers and FI as a question. When an inspector writes C1, C2 or C3 against an observation, they are stating a conclusion: this is dangerous, this is potentially dangerous, this could be improved. An FI states the opposite — that a firm conclusion is not yet possible. The inspector has seen enough to be concerned, but not enough to say how concerned, and the honest course is to record that openly rather than guess. This is why an FI should always come with a clear note of what needs investigating and why: a useful FI tells the next electrician exactly where to look, whereas a bare FI with no explanation leaves everyone none the wiser. Understood this way, the code is less an alarm than an instruction to go and find out — and the urgency attached to it reflects the fact that an unanswered safety question deserves the same care as a confirmed fault until it is resolved.
When an FI is used
An FI typically arises where the standard inspection and testing throws up an anomaly that needs more work to understand. Examples of situations that might lead to an FI include:
- A test result that does not make sense on its own and needs further checks to explain.
- Part of the installation that was not accessible during the inspection but shows signs that warrant a closer look.
- An unusual or non-standard arrangement whose safety cannot be confirmed without investigation.
- Evidence of a possible fault — such as a sign of past overheating — whose cause is not yet clear.
The key point is that an FI is not the inspector hedging. It is a legitimate code for a genuine, unresolved concern that the inspection alone could not settle, and it should be followed up promptly.
What these situations have in common is that the limitation lies in the inspection, not in the inspector's understanding of electrical safety. The item could be perfectly fine or genuinely dangerous; the point of the FI is that the standard visit did not provide enough information to say which. That is a different thing from indecision, and a well-written report makes the distinction obvious by stating precisely what additional work would resolve the question, so that the follow-up is a defined task rather than an open-ended search.
What happens after an FI is issued
Because the report is unsatisfactory while an FI is outstanding, the next step is to carry out the further investigation the code calls for. A qualified electrician examines the flagged item more closely — additional testing, opening up the installation, or checking the inaccessible part — and reaches a conclusion. The investigation can have several outcomes:
- The concern is resolved and the item is found to be satisfactory.
- It is reclassified as a C3 improvement recommendation.
- It is reclassified as a C2 (potentially dangerous) or C1 (danger present), in which case remedial work is needed.
For privately rented homes in England, the 2020 Electrical Safety Standards Regulations require further investigative work to be carried out within 28 days of the report (or sooner where specified), in the same way as remedial work — so an FI cannot simply be left. For owner-occupiers there is no statutory deadline, but the wording "without delay" makes clear it should be followed up promptly. Once the investigation is complete and any resulting work is done, the installation can be confirmed satisfactory.
Why a good report keeps FI codes to a minimum
An FI is a legitimate and necessary code, but a report that is littered with FI codes can be a sign of a rushed or limited inspection rather than a genuinely complicated installation. It is worth understanding the difference, because too many FI items can leave you paying for a second visit to resolve questions that a thorough inspection might have answered first time.
FI codes are appropriate where:
- An anomalous test result genuinely needs further checks to explain.
- A part of the installation was genuinely inaccessible and showed signs warranting a closer look.
- A non-standard arrangement cannot be assessed without opening it up or carrying out extra testing.
They are less appropriate when used as a catch-all for items the inspector could reasonably have examined during the visit. A well-conducted EICR records its extent and limitations clearly, so you can see why each FI was raised and what investigation it calls for. If a report comes back with numerous vague FI codes and little explanation, it is reasonable to ask the inspector to set out exactly what each one requires — and, where the items were accessible, why they were not resolved during the inspection itself.
Handled properly, an FI protects you: it ensures a genuine uncertainty is followed up rather than waved through. The aim is simply that each FI represents a real, unavoidable question, not a gap left by a cursory look.
Frequently asked questions
Does an FI code fail an EICR?
Yes. An FI (further investigation required) makes the overall result unsatisfactory, because the safety of the flagged item is unconfirmed. It is treated as seriously as a known fault until the further investigation determines what the issue actually is.
What's the difference between FI and C2?
A C2 is a known, understood fault classed as potentially dangerous. An FI is an unresolved concern the inspection could not fully assess — the inspector needs to investigate further before they can say whether it is a C1, C2, C3 or nothing at all.
What do I do about an FI on my report?
Arrange the further investigation the code calls for, carried out by a qualified electrician. It may confirm the item is fine, or reclassify it and require remedial work. For rented homes in England this must be done within 28 days; owner-occupiers should still act promptly.
Sources & further reading
- Electrical Safety First — EICR codes including FI
- NICEIC — EICR classification and further investigation
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property. They are guidance, not a quotation. Legal duties are summarised for guidance — confirm the current position on GOV.UK.