Does an FI make the EICR "unsatisfactory"?

Not on the current form. The BS 7671:2018+A4:2026 model EICR says C3 and FI observations are advisory and do not affect the overall assessment; only C1 or C2 make it unsatisfactory. Older forms required FI to be marked unsatisfactory, which is why many people still believe it does. If the investigation is likely to find danger, that is a sign the observation should be coded C1 or C2 now.

Can I use FI just because I ran out of time?

No. FI is for genuine evidence gaps — typically caused by access restrictions, occupied equipment, hidden runs, or ambiguous symptoms — not by inspector time pressure. If you ran out of time, the correct response is to either complete the inspection in a follow-up visit (and not yet issue the EICR), or to record the limitation explicitly in the report's "Extent and Limitations" section.

What's the difference between an FI and a "limitation" in the report?

A limitation is something the inspector and responsible person agreed would not be inspected (e.g., loft cables not accessible, sealed inaccessible junction box). It is recorded in the "Extent and Limitations" section, not Section K. An FI is something the inspector started to inspect but couldn't conclude on — there is positive evidence of a potential defect, just not enough to classify. FIs always go in Section K with an FI code.

How long does the responsible person have to complete an FI investigation?

For rented homes in England (private and social), the 2020 Regulations require further investigative work named in the report to be carried out within 28 days, or a shorter period if the report specifies one. For owner-occupied homes there is no statutory deadline, but the follow-up should happen within weeks.

Can I write "FI — investigate further" with no detail?

You can — but you shouldn't. A vague FI gives the responsible person nothing to commission and the follow-up electrician nothing to scope. A good FI specifies WHAT was observed, WHAT cannot be determined, WHAT tests/inspections are needed, and WHO is competent to do them. A vague FI tends to sit unresolved for months.

Should I issue a new EICR after the FI is closed, or supplement the original?

Industry practice varies. Some inspectors issue a supplementary observation document that attaches to the original EICR (preserving the inspection date and original observations). Others re-issue a full EICR once the investigation is complete. Either is acceptable provided the audit trail is clear and the responsible person, tenant (where applicable) and local authority can see both the original and the conclusion. The rented sector Regs require written confirmation of remedial / follow-up work in either form.

EICR OBSERVATION CODE

EICR Code FI — Further Investigation Advised

FI is the EICR code that says "I can't determine the correct classification without more work." It's used when access, equipment in service, or ambiguous symptoms prevent the inspector from confirming whether a defect is C1, C2 or C3. This guide explains exactly when FI is the correct call and how to scope the follow-up so it actually gets done.

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9 min readUpdated 2026-10-28Andrew Moore, Founder of Elec-Mate

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.

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The short answer

What does FI mean on an EICR?

FI stands for "further investigation is advised". The inspector has seen evidence of a possible defect but could not confirm whether it is C1, C2 or C3 on the visit. On the BS 7671 A4:2026 model EICR an FI is advisory and does not make the report unsatisfactory; only C1 or C2 do. Landlords in England must still complete the investigation within 28 days.

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Key takeaways

01On the BS 7671:2018+A4:2026 model EICR, FI means "Further investigation is advised". Earlier forms said "Further investigation required without delay".
02Under the A4 form, an FI does not make the report unsatisfactory. Section E states that C3 and FI observations are advisory and do not affect the overall assessment; only C1 or C2 make it unsatisfactory.
03For landlords of rented homes in England (private, and since 2025 social), the Electrical Safety Standards in the Private Rented Sector and Social Rented Sector (England) Regulations 2020 still require further investigative work named in the report to be done within 28 days, or sooner if the report says so.
04FI is used sparingly. Every observation should be assigned C1, C2 or C3 where evidence supports it — FI is for cases where evidence is genuinely incomplete.
05Common FI scenarios: live circuit prevented testing, hidden cable run, suspected fault behind permanent fixtures, audible signs of an issue with no visible defect, intermittent symptoms reported by occupants.
06A properly written FI specifies WHAT needs investigating, WHAT tests or inspections are needed, and WHO is competent to perform the follow-up.
07FI observations are recorded in Section K of the EICR alongside any C1/C2/C3 observations.

01 · EICR Observation Code

What FI Means

The A4:2026 model EICR defines FI as "Further investigation is advised". It indicates the inspector has found evidence of a potential defect but cannot confirm the right classification (C1, C2 or C3) without inspection or testing that was not possible on the visit. Forms before A4 used the wording "Further investigation required without delay".

FI is a deferred classification, not "no defect"

FI is not "I think there might be something." FI is "there's evidence of a potential defect that I cannot fully investigate today — and this needs follow-up before a safety conclusion can be drawn." If you cannot articulate WHAT to investigate, FI is the wrong code.

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02 · EICR Observation Code

When FI is the Correct Code

FI is reserved for scenarios where the inspector cannot make a final classification within the scope of the current visit. Common legitimate uses:

Live equipment that could not be isolated for testing during the inspection visit (e.g., 24-hour-essential medical equipment, occupied operating theatre, life-safety system that cannot be powered down).
Cable runs hidden behind permanent finishes (lath-and-plaster, panelled walls, accessible-only-with-destructive-access ducting) where visible symptoms suggest a fault.
Audible signs (humming consumer unit, sporadic arcing sounds) with no visible defect during the inspection window.
Occupant-reported intermittent symptoms (tripping breakers, flickering lights, smell of burning) that the inspector did not witness during testing.
Test results outside expected range with no immediately apparent cause (insulation resistance dropping over the test period, Zs values fluctuating).
Suspected borrowed neutral or shared CPC where definitive identification requires a circuit-by-circuit isolation sequence that was not possible.
Concealed appliance behind a fitted kitchen unit where the appliance circuit is showing fault symptoms.

03 · EICR Observation Code

Effect on the Overall EICR Assessment

This is the part that changed with Amendment 4. Section E of the A4:2026 model EICR says an unsatisfactory assessment indicates that C1 and/or C2 conditions have been identified, and that C3 and FI observations are advisory and do not affect the overall assessment but should be given due consideration. The amendment's own summary of changes puts it as "the code FI no longer needs to be marked as unsatisfactory".

Report with FI but no C1 or C2: the overall assessment is satisfactory on the A4 form.
Report with FI and any C1 or C2: unsatisfactory, because of the C1 or C2.
Older (A2/A3) EICR pads still carry the old notes that made FI unsatisfactory. Use the current form.
Rented homes in England (private and social): the 2020 Regulations require any further investigative work the report calls for to be completed within 28 days (or a shorter period stated in the report), with written confirmation to the tenant and the local authority. The legal duty attaches to the work, not to the word unsatisfactory.

Don't use FI to delay a decision

FI is not a "tomorrow problem" escape hatch. If the evidence at the time of inspection supports C1 or C2, use that classification — even if the inspector would like more data. FI is for genuine evidence gaps, not commercial convenience.

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04 · EICR Observation Code

How to Write an FI That Actually Gets Done

A vague FI ("further investigation recommended on socket circuit") is almost useless — the follow-up electrician has no scope, the responsible person can't commission the work, and the original inspector has provided no value. A good FI specifies four things:

WHAT was observed (the symptom or condition that triggered the FI).
WHAT cannot be determined without further work (the specific gap in evidence).
WHAT tests or inspections are needed to close the gap (insulation resistance after isolation, thermographic survey, lift-and-inspect specific fitting, etc).
WHO is competent to do the follow-up (a qualified electrician with relevant experience; in some cases a specialist contractor — e.g., a thermographer for thermal-imaging surveys).

Example of a good FI observation

"Consumer unit at meter cupboard shows audible humming under load. No visible damage to enclosure or terminals during visual inspection. Insulation resistance test could not be performed as the property was in occupation and prior notice of isolation was not given. Further investigation required: isolate the installation overnight, perform full insulation resistance test at 500 V, inspect all consumer unit terminals for tightness and signs of overheating, and remove and inspect main switch. Work to be carried out by a competent electrician with EICR experience within 28 days."

05 · EICR Observation Code

What Happens After an FI

Once the further investigation is complete, the inspector (or follow-up electrician) issues a supplementary observation document that converts the FI into its final classification:

If investigation reveals a C1 condition → immediate remedial action / isolation, supplementary observation recorded.
If investigation reveals a C2 condition → urgent remedial action on the 28-day timeline for rented homes or as agreed (owner-occupied).
If investigation reveals only a C3 issue → improvement recommendation logged.
If investigation finds no defect → the FI is closed and recorded as such.
The supplementary observation is retained alongside the original EICR for the duration of the certificate validity.

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