Heatline C24 Fault codes & diagnostics

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

Combi Natural Gas 24 kW Discontinued
GC Numbers 47-157-0747-157-06
Download the Heatline C24 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

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

Just want the most common Heatline C24 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 3 documented codes

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1%

Your boiler is struggling to detect the outside temperature, so it may not be adjusting its heating levels as efficiently as usual.

Low Engineer only £120-180

Parts commonly replaced

  • Outdoor temperature sensor
  • Wiring loom
Full explanation for 1%
Fault on DHW sensor

Your boiler is struggling to detect the temperature of your hot water supply, so it has turned off the tap water heating as a precaution.

Medium Engineer only £120-200

Parts commonly replaced

  • DHW NTC Sensor
  • Wiring harness
Full explanation for Fault on DHW sensor
Overheat Thermostat

Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Central heating pump
  • Diverter valve
  • PCB
Full explanation for Overheat Thermostat