Fault finding is detective work. The symptom you see, an RCD that trips at random, a circuit that is suddenly dead, lights that flicker when the kettle goes on, is rarely where the actual problem lives. The cause might be a nail through a cable, moisture in an outside socket, a loose neutral in a junction box under the floor, or an appliance that only leaks current when it warms up.
The wrong way to handle a fault is to swap parts until the symptom goes away. That wastes money and leaves the real defect in place, getting worse. The right way is systematic: split the circuit, measure insulation resistance and continuity, and follow the numbers until the fault has nowhere left to hide.
We handle fault finding across Greater London for homeowners, landlords and small businesses. Intermittent faults, the ones that never misbehave while an electrician is standing there, are our least favourite and our most common, and we have strategies for those: sectioning circuits, monitoring, and honest conversations about the most probable cause when certainty needs more than one visit.
What's included
Structured diagnosis, not part-swapping
We start with your description of the symptom (when it happens, what else is on, weather, recent work in the house), then test methodically: insulation resistance, continuity, loop impedance and RCD tests to isolate the faulty section.
Appliance versus installation separation
A large share of tripping RCDs are caused by an appliance, not the wiring. We establish early which side of the socket the problem is on, so you do not pay for wiring investigation when the culprit is the tumble dryer.
Repair in the same visit where possible
Once found, most faults are quick to fix: a burnt termination remade, a damaged section of cable replaced, a waterlogged outside fitting swapped for a properly rated IP66 one. We carry common parts to finish the job there and then.
Honest reporting on what we find
You get a clear explanation of the cause and what we did. If the fault is a symptom of ageing wiring, we say so with evidence, not scare tactics.
Testing and certification of repairs
Repaired circuits are retested to BS 7671 before being put back in service, with a Minor Works Certificate issued where applicable.
How the job runs
- 1
Describe the symptom
The more detail the better: what trips or fails, how often, at what time of day, in what weather, and anything that changed recently (new appliance, garden work, a leak). Half of diagnosis happens in this conversation.
- 2
Agree the price basis
Fault finding is charged from £80 covering the visit and first period of diagnosis, and we agree how to proceed before any longer investigation, so you are never on an open-ended meter.
- 3
Test and isolate
On site we section the installation and follow the test readings to the faulty circuit, then the faulty section, then the faulty accessory, joint or cable.
- 4
Repair
We fix the cause, remake or replace what failed, and deal with any collateral damage such as heat-damaged terminations either side of the fault.
- 5
Retest and explain
The circuit is retested, the RCD is verified, and we walk you through what happened and how to avoid a repeat, with paperwork for the repair.
What it costs
Fault finding starts from £80, and most jobs complete between £80 and £250. The spread is honest: some faults reveal themselves in twenty minutes, others hide in a junction box under a tiled floor. Time is the main cost driver, followed by parts and access (lifting carpet and boards takes longer than testing at accessible accessories).
For genuinely intermittent faults we agree a staged approach with you: an initial diagnostic visit at the standard price, and a plan for the next step if the fault refuses to show itself. Prices for any repair beyond the diagnosis are confirmed before the work is done.