Biasi Garda M90f Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2002-2007 Discontinued

Replaced by: Garda HE

Choose your boiler type

The Garda M90f range comes in 4 types

Pick the one you have. The fault codes, GC numbers and manual differ by type.

24SR 1 codes · 1 GC number 28SR 1 codes · 1 GC number 24S 1 codes · 1 GC number 28S 1 codes · 1 GC number
Each model has its own manual A family spans several manuals, one per model or generation. Pick your model above and its page has the manual its fault codes were read from.

The fault code is already on your display

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

Fault codes

All 1 documented codes

Tap any card for details

lock-out light

Your boiler has shut down for safety because it either failed to light, sensed it was getting too hot, or detected an issue with how it clears waste gases.

High DIY-safe £100-350 Shared across the Garda M90f. range

What to check first

  1. Check that your gas pre-payment meter (if applicable) has credit.
  2. Ensure any external gas isolation valves are fully open.
  3. Press and release the reset button on the front control panel to see if the boiler restarts.

Parts commonly replaced

  • Ignition Electrode
  • Safety Thermostat
  • Air Pressure Switch
  • Gas Valve
Full explanation for lock-out light
Status & diagnostic codes

4 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

1 second ON 1 second OFF Status Your boiler has detected that the temperature is low and is running its internal protection mode to prevent the pipes from freezing. 10 Diagnostic Your boiler has detected an issue with the air intake or exhaust system, which prevents it from operating safely. 12 Diagnostic Your boiler has detected an issue with the electrical circuit board or its internal wiring, preventing it from operating correctly. A short pulse every 4 seconds Status Your boiler is currently switched off but is monitoring the temperature to prevent the internal pipes from freezing.