Potterton Kingfisher MF 40-100 Fault codes & diagnostics

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

Regular Natural Gas 11.7-29.3 kW 2001-2007 Discontinued
GC Numbers 41-590-5441-590-5541-590-5641-590-5741-590-5841-590-59

Replaced by: Promax SL

The fault code is already on your display

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.
5 Emergency 4 High

All 9 documented codes

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Red LED

Your boiler has become too hot and has automatically switched itself off as a safety precaution.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • PCB
Red LED (Illuminated)

Your boiler has shut down because it has either become too hot or detected that dangerous exhaust fumes are not escaping correctly through the chimney.

Emergency Engineer only £90-250

Parts commonly replaced

  • Overheat Thermostat
  • TTB (Flue Monitoring) Sensor
  • Pump
  • Heat Exchanger cleaning
Red LED (Lockout)

Your boiler has automatically shut down for safety because it has detected a blockage in the chimney or flue that prevents dangerous exhaust gases from escaping.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue Thermostat (TTB)
  • Flue system components
Red LED (Overheat)

Your boiler has become too hot and has automatically switched itself off to prevent damage, meaning you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • PCB
Red LED (TTB)

Your boiler has sensed a problem with the dangerous exhaust gases escaping, so it has automatically shut itself down to keep your home safe.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue Thermostat
  • Flue Terminal
  • Fan
Red LED illuminated

Your boiler has become too hot and has automatically shut itself down as a safety precaution.

High DIY-safe £90-180

What to check first

  1. Locate the reset button on the control panel, usually hidden under a small plastic cap or recessed.
  2. Press the reset button firmly to clear the lockout.
  3. Check that your radiator valves are open and that the pump is running to prevent it from overheating again.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistor
Red LED illuminated (Lockout)

Your boiler has detected that fumes are not escaping properly through the flue and has shut itself down for your safety.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flue Thermostat (TTB)
  • Flue pipe assembly
  • Flue terminal
Red LED illuminated (Overheat)

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
  • Pump
  • PCB
Red LED illuminated (TTB)

Your boiler has detected potentially dangerous exhaust fumes backing up into your home due to a blocked or obstructed chimney or flue, and has safely shut itself off to prevent carbon monoxide poisoning.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue or chimney terminal
  • Flue gathering hood
  • TTB sensor

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