EV Charger Fault Finding: Error Codes, Communication Failures, Supply and Earth Faults

Quick Answer: Most domestic EV charge-point (EVSE) faults fall into four groups: supply faults (no power, tripped circuit), communication faults (the Control Pilot handshake between charger and car fails), earth/PEN faults (the open-PEN protection device or RCD trips), and device faults (overtemperature, contactor, locked cable). All UK installs follow BS 7671:2018+A2:2022 Section 722, which requires 6 mA DC fault detection (a built-in RDC-DD or a Type B RCD). Start at the consumer unit, confirm the protective device type, then work along the Control Pilot signal to the vehicle.

Summary

An EV charger that "won't charge" is rarely a single thing. The charger sits between the building's electrical supply and a sophisticated, communicating vehicle, and a fault anywhere in that chain shows the same outward symptom — no charge and a flashing light. Effective diagnosis means splitting the problem into supply side, communication side, earthing/protection side, and the unit itself, then testing each in turn rather than guessing.

The UK-specific complications are earthing and DC fault protection. Because most homes are on a PME (TN-C-S) supply, an open-PEN fault could make the car's body live, so the charger must either include open-PEN protection or use an alternative earthing arrangement (earth rod / TT). And because EVs can inject DC into the supply, BS 7671 Section 722 requires 6 mA DC fault detection — either a residual direct current device (RDC-DD) built into the charger or a Type B RCD. A surprising number of "nuisance trips" are actually the open-PEN device doing its job during a voltage excursion, or a Type A RCD reacting to DC it cannot handle.

The other UK reality is brand-specific error codes. Beyond the universal symptoms, each manufacturer's app and LED pattern means something different, so the manufacturer manual is part of the toolkit. This article gives the brand-agnostic diagnostic logic; finish with the specific unit's code list.

Key Facts

Quick Reference Table

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Symptom First check Likely causes
Dead unit, no lights Circuit breaker / isolator Tripped MCB/RCBO, isolator off, supply fault
Trips on plug-in / mid-charge RCD type & open-PEN device Type A vs Type B, 6 mA DC fault, PEN excursion, earth fault
Lights on, won't start charge CP signal / vehicle Communication fault, vehicle not requesting, locked connector
Charges slowly / derates CT clamp & temperature Load management active, hot connection, derating
"Charging" but car not PP/CP & cable Cable fault, connector dirty, vehicle setting
Won't charge at certain times Smart schedule Off-peak window / app schedule (not a fault)
Cable won't release Lock solenoid / vehicle Vehicle still locked, solenoid fault, power-cycle

Detailed Guidance

Master decision tree

EV CHARGER WON'T CHARGE
=======================
1. Any status lights at all?
   NO  -> SUPPLY SIDE
          - Check dedicated MCB/RCBO at consumer unit (reset once)
          - Check rotary isolator / built-in isolator
          - Check tails/connections; confirm 230 V at unit
          - Still dead -> internal PSU/contactor fault (manufacturer)
   YES -> go to 2

2. Does it trip the protective device?
   YES -> EARTH / PEN / RCD branch (see below)
   NO  -> go to 3

3. Plug in the car. Does it move to "connected" then "charging"?
   Stops at CONNECTED (won't charge) -> COMMUNICATION branch
   Reaches CHARGING but no energy   -> CT/load mgmt or vehicle branch
   Won't even reach CONNECTED        -> PP/cable detection / connector

Supply-side branch

SUPPLY FAULTS
-------------
[ ] Dedicated circuit breaker ON and not tripped
[ ] Isolator switch ON (separate rotary or integral)
[ ] 230 V present at the unit's incoming terminals
[ ] Terminal tightness (loose tails = heat, derating, intermittent)
[ ] No upstream main-switch / supply issue
If supply present at unit but unit dead -> internal fault:
   PSU, contactor, or controller. Manufacturer diagnostics / RMA.

Earth / PEN / RCD branch (the UK specials)

TRIPPING FAULTS
---------------
First identify the protection:
  - Charger has built-in RDC-DD (6 mA)?  upstream is usually Type A.
  - No RDC-DD?  upstream must be Type B RCD.
  - Open-PEN device fitted (PME supply) OR TT/earth rod used?

If it trips:
  [ ] Open-PEN device latched? It disconnects on a line/neutral
      voltage excursion (e.g. utility PEN issue). Reset; if it
      re-trips with no load, suspect a real supply voltage fault
      -> report to DNO.
  [ ] Type A RCD + EV with DC leakage -> nuisance trips. Confirm
      the unit's RDC-DD is healthy; a failed RDC-DD shifts DC to
      the AC RCD.
  [ ] Real earth fault: insulation-resistance test the circuit and
      the connector; check for water ingress at the unit/cable.
  [ ] Verify Zs and earthing arrangement is correct for the supply
      type (never bond the EV earth to a PME earth without an
      approved PEN-fault solution).

Communication branch (Control Pilot)

COMMUNICATION FAULTS (reaches "connected", won't charge)
--------------------------------------------------------
The CP handshake sets a PWM duty cycle = available current. If it
fails, the car won't draw power.
[ ] Try a different vehicle or a known-good cable (untethered) to
    isolate charger vs car vs cable.
[ ] Inspect connector pins for corrosion/debris/bent pins (CP/PE).
[ ] Check the protective-earth (PE) continuity to the connector -
    the car checks PE before charging; a broken earth blocks it.
[ ] Power-cycle the unit (and the car) - clears latched CP states.
[ ] App/firmware: confirm not stuck mid-update; update if behind.
[ ] If CP signal is out of spec (measurable) -> charger control
    board fault (manufacturer).
A common real-world cause: the EARTH path is broken (open-PEN
device tripped, or PE not made off), so the car refuses to charge
even though "power" is present.

CT / load-management and "slow" branch

SLOW OR THROTTLED CHARGING
--------------------------
[ ] CT clamp around the main tail correctly oriented & connected?
    A misread CT makes the unit think the house is at max load and
    it backs the EV current right off.
[ ] Hot connector/cable -> unit derates for safety. Check plug,
    tails and terminal torque; replace damaged cable.
[ ] Vehicle current setting / battery near full / cold battery
    (the car limits acceptance, not a charger fault).
[ ] Off-peak smart schedule limiting the window.

Don't mistake a schedule for a fault

Under the Electric Vehicles (Smart Charge Points) Regulations 2021, units ship with default off-peak charging windows. A "it won't charge in the afternoon" complaint is frequently the smart schedule, not a fault — check the app/schedule before chasing hardware.

Frequently Asked Questions

Why does my EV charger keep tripping the RCD?

Three common UK causes: (1) the upstream RCD is a Type A but the charger's built-in 6 mA DC device (RDC-DD) has failed, so DC leakage reaches the AC RCD and trips it; (2) the open-PEN protection device is operating because of a real supply voltage excursion (sometimes a DNO/utility issue) or a fault; (3) a genuine earth fault from water ingress or cable damage. Identify the protection type first, then insulation-test the circuit and check the earthing arrangement.

The lights are on but the car won't charge — what now?

This is usually a communication (Control Pilot) problem or a broken earth path, not a power fault. The vehicle checks the protective-earth and the CP handshake before drawing current. Try a known-good cable or a different car to isolate the fault, inspect the connector pins, confirm earth continuity to the connector, and power-cycle both unit and vehicle. If the CP signal is out of spec, the charger's control board is suspect.

Do I need a Type B RCD for an EV charger?

You need 6 mA DC fault detection somewhere. If the charger has a built-in RDC-DD, an upstream Type A RCD is acceptable; if it does not, you must provide a Type B RCD. Fitting a plain Type AC RCD is non-compliant for EV charging. Always check the unit's specification before choosing the protective device.

What is open-PEN protection and why does it cut out?

On a PME (TN-C-S) supply, a broken combined neutral-earth (PEN) conductor in the network could raise the earth — and the car's metal body — to a dangerous voltage. Open-PEN protection monitors the supply voltage and disconnects the charger if it goes outside safe limits. If it trips with no load and re-trips on reset, suspect a real supply problem and report it to the DNO; it is a safety device doing its job, not a nuisance.

How do I read the error code?

The status LEDs and app messages are brand-specific — the same flash pattern means different things on different units. Use this article's logic to localise the fault to supply / communication / earth / device, then consult the specific manufacturer's manual or app to translate the exact code. Keep the model's documentation with the job notes.

Regulations & Standards