Electrical Fault Finding
& Diagnostics in London

Your legal duty to keep the installation safe

The rules that govern electrical safety in rented homes in England are set out in the Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020. They require landlords to ensure that national standards for electrical safety are met, to have every fixed installation inspected and tested at intervals of no more than five years, and to obtain a report from the person carrying out that inspection.

The part that matters most for diagnostics is what happens next. Where a report states that further investigative or remedial work is required, the landlord must ensure that work is carried out within 28 days, or sooner if the report specifies a shorter period. A code FI observation — “further investigation required without delay” — is not a pass with a note attached; it is an instruction to send somebody back with test equipment.

That duty does not go to sleep between inspections either. The standards have to be met throughout the tenancy, so a fault that appears in month eighteen of a five-year cycle has to be dealt with then, not deferred to the next inspection date. Local authorities also assess rented homes under the Housing Health and Safety Rating System introduced by the Housing Act 2004, and electrical hazards are among the matters they consider when deciding whether a property is fit to let.

For plain-English background on the risks behind the regulations, the charity Electrical Safety First publishes guidance for both landlords and householders on tripping devices, damaged accessories and safe use of electricity in the home.

Electrical fault finding and BS 7671

The testing itself follows BS 7671, the IET Wiring Regulations, which is the standard every UK electrician works to. BS 7671 sets out the sequence of tests used to prove an installation: continuity of protective conductors, continuity of ring final circuit conductors, insulation resistance, polarity, earth fault loop impedance and the operating time of residual current devices. Diagnostics uses the same tests as an inspection, but applies them selectively and repeatedly to isolate a single defect.

Insulation resistance testing is the workhorse. A test voltage is applied between live conductors and between each conductor and earth, and the resistance is measured in megohms. A healthy circuit reads comfortably above the minimum value in the standard. A circuit that reads low has a breakdown in insulation somewhere along its length — a cable pierced by a fixing, water sitting in an outdoor enclosure, a scorched terminal, or an appliance that has failed internally. Disconnecting the circuit at a mid-point and repeating the test halves the search area, and repeating that split three or four times usually lands on the fault.

Continuity testing proves that a conductor runs unbroken from one end of a circuit to the other, and that a ring final circuit is genuinely a ring rather than two spurs that were never joined. This is the test that finds the dead socket: a broken conductor, a terminal that was never tightened, or a cable that has been cut during building work will show up immediately as an open circuit where a fraction of an ohm was expected.

Landlord, agent and freeholder responsibilities

The duty for the fixed wiring — the consumer unit, the cabling, the sockets, switches and light fittings — sits with whoever owns and provides the installation. Where a managing agent runs the property, the day-to-day booking can be delegated by contract, but liability generally stays with the owner. It is worth having your management agreement say in writing who instructs a diagnostic visit and who signs off remedial work, because a fault reported on a Friday afternoon should not wait for a committee.

A tenant’s own appliances are a different matter. A kettle, a washing machine or a phone charger that leaks current to earth will trip the same device as a wiring fault, and the symptom looks identical from the consumer unit. Our engineers test with appliances disconnected and reconnected specifically to separate the two, and if the cause turns out to be a tenant’s appliance rather than your wiring, we will say so and show you the reading that proves it.

In a purpose-built block, the demise line matters. The consumer unit and everything downstream of it inside the flat is normally the leaseholder’s or landlord’s responsibility, while risers, landlord supplies and communal lighting belong to the freeholder or managing agent. If testing shows the fault sits outside your demise, we will document it so you can pass it to the right party rather than paying for somebody else’s cable.

Landlords, letting agents and homeowners

Anyone with an electrical symptom they cannot explain needs a diagnostic visit rather than a guess. For landlords, the trigger is usually a tenant report: the power keeps going off, half the kitchen sockets are dead, the bathroom light hums. For homeowners it is more often something that has crept up slowly — lights that dim on the washing machine cycle, or a breaker that has started tripping once a week when it never used to.

Letting agents call us for the awkward cases in between tenancies, where a property has been empty, something has been disconnected during works, and nobody is quite sure what changed. Void periods are the ideal time to trace an intermittent fault, because the whole installation can be isolated and tested without inconveniencing anybody.

A diagnostic call-out is also the right response to a report that has come back with observations you do not understand. If an inspection report has flagged a circuit for further investigation, that is a direct instruction to test, not a suggestion to monitor.

HMOs, flats, commercial and mixed-use premises

Houses in multiple occupation generate more diagnostic calls than any other property type we attend. More occupants means more appliances on each protective device, more extension leads, more heaters in winter, and a much higher chance of cumulative earth leakage tripping an RCD that has never given trouble before. Licensing conditions also tend to require faults to be remedied promptly, so an unexplained trip in an HMO is rarely something you can leave until next month.

Flats bring their own pattern. Shared risers, communal landing lights and a consumer unit tucked inside a hall cupboard mean the fault is not always where the symptom is, and coordination with the managing agent is sometimes needed before a circuit can be isolated at all.

Shops, offices, restaurants and mixed-use buildings run three-phase supplies, larger distribution boards and equipment that draws far more current than anything in a home, so diagnostics there takes longer and needs different equipment. If that describes your building, start with our commercial EICR service, which covers the periodic inspection side, and we will scope any fault finding around it.

How a diagnostic call-out differs from an EICR

The two are easy to confuse because they use the same test equipment. The difference is scope and purpose. An EICR certificate is a periodic inspection of the whole installation, sampled to a defined percentage, producing a formal report that says satisfactory or unsatisfactory. It is the document a landlord in England needs at least every five years. A diagnostic visit is unlimited in depth but narrow in width: we go as deep as necessary into one problem and produce a service sheet, not a certificate.

In practice they feed each other. An inspection that returns an FI code sends you to a diagnostic visit; a diagnostic visit that uncovers widespread deterioration sends you to a full inspection. If your certificate is close to expiry when you call us about a fault, booking both together saves a second visit and a second access appointment with the tenant.

Portable appliances are a separate exercise again. Where the leakage is coming from equipment rather than wiring, PAT testing identifies which item is at fault, and in blocks and HMOs the same visit often sits alongside fire alarm work. You can book any combination online and we will send one engineer wherever the qualifications allow it.

What happens once we have located the fault

There is no pass or fail on a diagnostic visit. What you get is a cause, a reading that supports it, and a decision to make. In practice the outcome falls into one of three groups:

• Repaired on the day. A loose terminal, a failed socket, a damaged accessory or a defective breaker can normally be put right inside the included hour using the spares our engineers carry. The circuit is retested and returned to service.
• Made safe, repair quoted. Where the defect needs materials we do not carry or work beyond an hour — a buried cable to replace, a section to rewire, a consumer unit that has reached the end of its life — the affected circuit is isolated and labelled so the rest of the property stays usable, and you receive a fixed-price quote.
• Not your wiring. Sometimes the answer is a tenant’s appliance, a neighbour’s supply, a communal circuit or a fault upstream of the meter that belongs to the distribution network operator. We document the evidence so you can send it to the right party.

Whichever applies, nothing is left in a dangerous condition. A circuit that cannot be made safe by repair is isolated before we leave, and both landlord and tenant are told in plain language what has been switched off and why.

Repairs, parts and re-testing

Our engineers carry the parts that account for most repairs: breakers, RCDs, sockets, switches, ceiling roses, connectors and cable. Where a specific or non-standard item is needed — a discontinued consumer unit module, a particular light fitting, a manufacturer’s part for a shower or immersion heater — we identify it on site, source it, and return at a time that suits the occupier.

Larger remedial work is always quoted in writing before it starts, itemised so you can see what is labour and what is materials. Nothing beyond the included hour proceeds without your approval, and if you would rather take the report and get comparison quotes, that is entirely reasonable — the diagnosis is yours either way.

After any repair the circuit is retested and the readings are recorded, so the paperwork shows the installation was proved safe rather than simply switched back on. If the work was substantial enough to affect your next periodic inspection, we will tell you, and you can book the follow-up visit online at the same time.