Johnson Starley C10d Fault codes & diagnostics

14 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Regular Natural Gas 10.4 kW 2001-2007 Discontinued
GC Number 42-416-99
Download the Johnson Starley C10d manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Each cell = one fault code. Hover to identify.
1 Emergency 12 High 1 Medium

All 14 documented codes

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13

Your boiler has been manually reset too many times in a single hour and has locked itself as a safety precaution.

High DIY-safe £0-120

What to check first

  1. Locate the main electrical power switch for the boiler (usually a fused spur near the unit).
  2. Switch the power OFF.
  3. Wait approximately 30 seconds.
  4. Switch the power back ON to clear the lockout.

Parts commonly replaced

  • None (Software reset)
  • Control PCB (if fault persists)
21

Your boiler's main control panel has developed an internal electrical error and can no longer process information correctly.

High Engineer only £250-£400

Parts commonly replaced

  • ESYS Control Board
  • Main PCB
25

Your boiler's internal computer parts are having trouble communicating because their software versions do not match.

High Engineer only £280-£450

Parts commonly replaced

  • ESYS Electronic Control Board
  • Main PCB

Related codes

26

Your boiler is struggling to keep its burner lit and has shut down for safety after failing to maintain a flame multiple times.

High Engineer only £120-350

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Fan
  • Ignition lead

Related codes

30

Your heater has detected a technical fault with its internal temperature sensor, causing the system to shut down for safety.

High Engineer only £100-190

Parts commonly replaced

  • Duct air temperature sensor (NTC)
  • Sensor wiring harness

Related codes

31

Your boiler has lost connection with its internal air temperature sensor, which means it cannot safely monitor the heat level and has stopped working.

High Engineer only £90-180

Parts commonly replaced

  • Duct air temperature sensor (thermistor)
  • Wiring harness

Related codes

34

Your boiler is not receiving the correct amount of electricity from your home's power supply to run safely and has shut down as a precaution.

High Engineer only £90-250

Parts commonly replaced

  • Electrical Wiring
  • Printed Circuit Board (PCB)
  • External Voltage Regulator
43

Your boiler's internal thermometer has developed an electrical fault, meaning the system can no longer safely monitor how much heat is returning to the unit.

High Engineer only £120-£240

Parts commonly replaced

  • Return air temperature sensor (thermistor)
  • Wiring harness
44

Your boiler's heat sensor has stopped communicating with the system, so the unit has shut down to prevent potential overheating.

High Engineer only £120-220

Parts commonly replaced

  • Return thermistor
  • Wiring harness

Related codes

45

Your boiler has detected an electrical fault with the sensor that monitors the exhaust gas temperature, causing it to shut down for safety.

High Engineer only £120-210

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

46

Your boiler has shut down because it cannot detect a signal from the sensor that monitors exhaust gases, preventing it from running safely.

High Engineer only £120-£210

Parts commonly replaced

  • Flue Gas Temperature Sensor (NTC)
  • Wiring Harness

Related codes

57

Your boiler is struggling to breathe, meaning it cannot pull in enough fresh air to safely burn the gas needed to provide heat and hot water.

Emergency Engineer only £150-350

Parts commonly replaced

  • Flue fan
  • Air pressure switch
  • Flue seals
  • Ventilation ducting

Related codes

99

Your boiler's main control panel is unable to communicate with the internal system, which has caused the unit to stop working.

High Engineer only £150-300

Parts commonly replaced

  • Interface cable
  • Main printed circuit board (PCB)
  • Display unit

Related codes

Lt

Your heater is temporarily shutting down because it is getting too hot and needs to cool down for safety.

Medium DIY-safe £60-140

What to check first

  1. Check all warm air grilles/vents are open and not blocked by furniture or curtains
  2. Inspect the air filter and clean or replace it if it is dusty
  3. Turn the heater off and back on to reset once it has cooled down

Parts commonly replaced

  • Air filter
  • Limit thermostat
  • Fan motor