Ferroli Tempra 12 18 Fault codes & diagnostics

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

Regular Natural Gas 12-18 kW Discontinued

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.
1 Emergency 10 High 1 Medium 7 Low
Just want the most common Ferroli Tempra 12 18 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 19 documented codes

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LED / flash-pattern codes
4 (Flashing Light)

Your boiler is currently in standby mode and is working exactly as it should while waiting for a signal from your thermostat to provide heating.

Low DIY-safe

What to check first

  1. Check your room thermostat is set to a higher temperature than the current room temperature
  2. Ensure your heating timer or programmer is currently in an 'ON' period
  3. Verify the central heating dial on the boiler front panel is not turned to the off position
Full explanation for 4 (Flashing Light)
4 (Flashing)

Your boiler is working correctly and is currently in standby mode, waiting for a signal from your thermostat or hot water tap to start.

Low DIY-safe

What to check first

  1. Check your room thermostat is set to a higher temperature than the current room temperature
  2. Ensure your heating timer or programmer is currently in an 'ON' period
  3. Turn up the heating dial on the front of the boiler if it is set too low
Full explanation for 4 (Flashing)
5 (Flashing Light)

Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.

High DIY-safe £0-£80

What to check first

  1. Locate the external filling loop, which is usually a flexible silver braided hose with one or two small valves underneath the boiler.
  2. Open the valves slowly to allow mains water into the system while watching the pressure gauge on the front panel.
  3. Close the valves tightly once the needle reaches the green zone, typically between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure gauge
  • Pressure relief valve
Full explanation for 5 (Flashing Light)
5 (Flashing)

Your boiler has stopped working because the water pressure inside the heating system has dropped too low.

Medium DIY-safe £0-90

What to check first

  1. Locate the filling loop, which is a silver braided hose with one or two valves connecting your boiler to the cold mains pipe.
  2. Open the valve(s) slowly to allow water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Ensure both valves are turned firmly off to prevent the system from over-pressurising.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor
Full explanation for 5 (Flashing)
Digital codes
Boiler locked-out

Your boiler has shut itself down as a safety precaution and needs a manual reset to try and start up again.

High DIY-safe £100-250

What to check first

  1. Check that the gas supply valve near the boiler and your gas meter are both in the 'on' position
  2. Locate the reset knob labeled 'A' on the boiler control panel
  3. Turn the knob to the 'Reset' position, hold briefly, then release it to allow the boiler to attempt ignition

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • Gas valve
  • PCB
Full explanation for Boiler locked-out
F1

Your boiler is unable to light its internal flame, which means you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Detection probe

Related codes

Full explanation for F1
F2

Your boiler has successfully lit, but it is unable to detect that the flame is actually burning, so it is shutting down for safety reasons.

High Engineer only £120-200

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • PCB

Related codes

Full explanation for F2
F3

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
  • System filter
Full explanation for F3
F4

Your boiler has detected an issue with its internal ventilation, meaning it cannot safely remove combustion gases, so it has shut down to prevent potential danger.

High Engineer only £120-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi
Full explanation for F4
F5

Your boiler has detected an issue with its internal airflow system that prevents it from starting safely.

High Engineer only £120-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan assembly
  • Venturi
Full explanation for F5
F6

Your boiler has lost the ability to read the temperature of the water being sent to your radiators, so it has shut down as a precaution to prevent overheating.

High Engineer only £120-200

Parts commonly replaced

  • Central heating flow temperature sensor
  • Wiring harness
Full explanation for F6
LED2

Your boiler has switched itself off for safety because it cannot ignite or has detected a potentially dangerous temperature spike.

Emergency Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Safety thermostat
  • PCB

Related codes

Full explanation for LED2
lockout light

Your boiler has stopped working as a safety precaution and needs a manual reset to try and start up again.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • PCB
  • Gas valve
Full explanation for lockout light
Red lockout light

Your boiler has stopped working as a safety precaution and needs you to manually restart it to try and clear the error.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • Gas valve
  • Printed circuit board
Full explanation for Red lockout light