Saunier Duval Themaclassic F25E Fault codes & diagnostics

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

Combi Natural Gas 25 kW 2003-2010 Discontinued

Replaced by: ThemaPlus F25E

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
15 High

All 15 documented codes

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Flashing pressure

Your boiler has detected that the water pressure level inside the heating system has dropped below the required amount to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate the filling loop, which is usually a silver braided hose with one or two small valves underneath the boiler.
  2. Slowly open the valves to allow mains water into the system until the pressure gauge needle reaches the green zone (typically 1.0 to 1.5 bar).
  3. Close the valves tightly to stop the flow of water and check the display to see if the flashing warning has cleared.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor
Red flashing light

Your boiler has detected a general issue and has entered a safety lockout mode.

High DIY-safe £100-250

What to check first

  1. Locate the On/Off switch on the boiler control panel.
  2. Turn the switch to the (0) position and wait for five seconds.
  3. Turn the switch back to the (I) position to attempt a system reset.

Parts commonly replaced

  • Ignition electrode
  • Printed Circuit Board (PCB)
  • Fan assembly
  • Pressure switch

Related codes

E01

Your boiler is failing to light the flame properly, so it has turned itself off for safety until it is repaired.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
E02

Your boiler is struggling to clear exhaust gases safely, so it has turned itself off to prevent any risk.

High Engineer only £120-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venture pipe
E03

Your boiler is failing to vent exhaust gases safely, so it has stopped working to prevent a hazard.

High Engineer only £120-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi nozzle
E05

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 sensor
  • Pump
  • PCB
E06

Your boiler has stopped working because it is unable to accurately measure the temperature of the water circulating through your radiators.

High Engineer only £120-180

Parts commonly replaced

  • NTC thermistor sensor
  • Wiring harness

Related codes

E09

Your boiler is struggling to accurately measure the water pressure inside the system, which is preventing it from firing up safely.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
E13

Your boiler's computer system has encountered an internal error and can no longer control the heating or hot water functions.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

E14

Your boiler has lost the ability to accurately measure the temperature of the hot water it is trying to produce, so it has shut down to prevent overheating.

High Engineer only £120-200

Parts commonly replaced

  • Hot water NTC thermistor

Related codes

E16

Your boiler is struggling to bring gas into the system to create a flame, so it has safely shut itself down to prevent any issues.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve assembly
  • Printed Circuit Board (PCB)

Related codes

E19

Your boiler has lost the connection to the sensor that monitors the temperature of your heating water, so it has shut down to prevent overheating.

High Engineer only £120-200

Parts commonly replaced

  • NTC sensor (Temperature probe)
  • Wiring harness
E26

Your boiler has detected that the water temperature is significantly different between the start and end of its heating circuit, which suggests the water is not circulating properly.

High Engineer only £150-250

Parts commonly replaced

  • NTC thermistors
  • Circulation pump
  • Diverter valve

Related codes

F1

Your boiler is attempting to start up, but it is unable to keep the flame alight once it ignites, so it safely shuts itself down.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Gas valve
  • Ignition lead
  • Printed circuit board (PCB)

Related codes

F4

Your boiler is attempting to start its flame but is unable to stay lit, causing it to shut down for safety reasons.

High Engineer only £120-250

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes