Diagnose
Electrical faults by symptom
A quick homeowner's diagnostic reference. Match what you're seeing, hearing or smelling to the most likely causes, and check whether it needs isolating right now or can be investigated soon. When in doubt, isolate at the consumer unit and call.
Burning or fishy smell near a socket, switch or consumer unit
Isolate nowLikely causes
- Loose terminal arcing under load (the classic melted-neutral cause)
- Overheating conductor or accessory
- Failing plastic housing on an older accessory
What to do
Isolate the circuit at the consumer unit immediately and call an electrician. Do not keep using the outlet — this is the number-one precursor to an electrical fire.
RCD or RCBO trips as soon as it is reset
Investigate soonLikely causes
- Persistent earth fault on one circuit (damaged cable, faulty appliance, water ingress)
- Faulty RCD/RCBO itself (less common)
What to do
Unplug every appliance on the affected circuit and try to reset. If it holds, plug items in one at a time. If it still trips with nothing plugged in, the fault is in the fixed wiring — call an electrician.
RCD trips intermittently, often at the same time of day
Investigate soonLikely causes
- Cumulative earth leakage from several appliances (freezer, washing machine, immersion)
- Moisture in an outdoor circuit after rain
- Nuisance tripping from an old 100 mA whole-house RCD
What to do
Log which appliances are running when it trips. Modern practice is to split circuits onto individual 30 mA RCBOs so one fault doesn't kill the whole board.
Warm or discoloured socket / plug top
Isolate nowLikely causes
- Loose terminal inside the socket
- Undersized or damaged flex on a high-load appliance (kettle, heater, tumble dryer)
- Worn socket contacts no longer gripping the plug pins
What to do
Stop using the socket, isolate the circuit and get the accessory replaced. Warmth = resistance = the start of a burnout.
Lights flicker when appliances switch on
Investigate soonLikely causes
- Voltage drop from a heavy load starting up (shower, cooker, kettle)
- Loose neutral in the consumer unit or DNO cut-out
- Failing driver on LED lights (dimmer incompatibility)
What to do
Occasional dip when a shower fires is normal. Persistent flicker across the whole house — especially with a burning smell or browning of light bulbs — can indicate a loose service head neutral and needs urgent investigation.
Buzzing or humming from a switch, socket or dimmer
Investigate soonLikely causes
- Overloaded or incompatible dimmer driving LED lamps
- Loose terminal vibrating under AC current
- Failing transformer or LED driver
What to do
Persistent buzzing warrants a look — a loose terminal that buzzes today typically becomes a burning smell tomorrow.
Half the house has no power but the main switch is on
Investigate soonLikely causes
- One RCD has tripped and taken all circuits on that side of a split-load board
- Loose neutral bar
What to do
Check the consumer unit — reset the tripped RCD. If it won't reset or trips again immediately, follow the earth-fault steps above.
Mild tingle when touching a metal appliance or tap
Isolate nowLikely causes
- Earthing / bonding fault
- Faulty appliance leaking to its metal case
What to do
Stop using the appliance and isolate the circuit. This is dangerous — a proper earth path is missing. Call an electrician the same day.
Sockets or switches with visible cracks, scorch marks or brown staining
Isolate nowLikely causes
- Long-standing overheating
- Impact damage exposing live parts
What to do
Isolate the circuit and replace the accessory before further use.
MCB trips only when a specific appliance is used
MonitorLikely causes
- Faulty appliance drawing overcurrent
- Undersized MCB for the actual load
What to do
Test with a known-good appliance in the same socket. If the MCB still trips, the circuit or MCB is the issue; if it holds, the original appliance is the fault.