Johnson Starley C16d Fault codes & diagnostics

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

Regular Natural Gas 16.1 kW 2006-2009 Discontinued
GC Number 42-415-19

Replaced by: Quantom

Download the Johnson Starley C16d manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 11 High 1 Medium
Just want the most common Johnson Starley C16d faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 13 documented codes

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13

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

Medium DIY-safe £0-120

What to check first

  1. Turn off the power supply to the boiler at the fused spur switch.
  2. Wait for at least 60 minutes without touching the controls to allow the internal timer to reset.
  3. Restore power and attempt one single manual reset on the boiler unit itself.

Parts commonly replaced

  • No parts usually required
  • PCB (if timer circuit is faulty)
Full explanation for 13
21

Your boiler's internal computer is having trouble processing signals from its electronic sensors, which has caused the system to shut down for safety.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Control Module
Full explanation for 21
25

Your boiler's internal computer chips are failing to communicate correctly because of a software conflict or a hardware memory error.

High Engineer only £250-£450

Parts commonly replaced

  • ESYS Control Board
  • Main PCB

Related codes

Full explanation for 25
26

Your boiler is struggling to keep its flame lit and has shut down for safety after failing to stay ignited five times in a row.

High Engineer only £120-350

Parts commonly replaced

  • Flame sensing electrode
  • Ignition control board
  • Gas valve
  • Fan
Full explanation for 26
30

Your boiler has stopped working because it has detected an electrical fault with the internal sensor that monitors air temperature.

High Engineer only £120-210

Parts commonly replaced

  • Duct air temperature sensor
  • Wiring harness

Related codes

Full explanation for 30
31

Your boiler has lost its connection to the sensor that monitors air temperature, preventing it from heating up safely.

High Engineer only £90-160

Parts commonly replaced

  • Duct air temperature sensor
  • Wiring harness

Related codes

Full explanation for 31
34

Your boiler is not receiving enough electrical power from your home's supply to operate safely.

High Engineer only £90-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Electrical wiring harness
  • Voltage protector/regulator
Full explanation for 34
43

Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the air returning to the unit, causing it to shut down for safety.

High Engineer only £120-210

Parts commonly replaced

  • Return air temperature sensor (thermistor)
  • Wiring harness
  • Control board
Full explanation for 43
44

Your boiler has detected a disconnection in the sensor that monitors the air returning to the unit, causing it to stop operating as a safety precaution.

High Engineer only £120-200

Parts commonly replaced

  • Return air temperature sensor
  • Wiring harness

Related codes

Full explanation for 44
45

Your boiler has detected a technical fault with the sensor that monitors exhaust gases, causing the system to shut down for safety.

High Engineer only £120-240

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness
  • Control PCB

Related codes

Full explanation for 45
46

Your boiler has stopped working because it cannot detect the temperature of the exhaust gases, causing it to shut down for safety.

High Engineer only £120-190

Parts commonly replaced

  • Flue gas temperature sensor (NTC)
  • Wiring harness

Related codes

Full explanation for 46
57

Your boiler is struggling to breathe, likely because the internal fan cannot move enough air to safely vent combustion gases outside.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flue fan
  • Air pressure switch
  • Flue assembly seals

Related codes

Full explanation for 57
99

Your boiler has lost the ability for its main control panel to talk to the internal electronic brain, meaning it cannot receive instructions to fire up.

High Engineer only £150-300

Parts commonly replaced

  • Interface cable
  • Main PCB
  • User interface display unit

Related codes

Full explanation for 99