ALARM 03 Emergency

Sime ALARM 03 Fault Code

Also written as ALARM03 — same fault.

The Sime ALARM 03 fault code means: your boiler has too much water inside it, causing the pressure to rise to an unsafe level.. It appears on 1 Sime model in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: High system pressure (above 2.8 bar) — drain via drain valve until 1.0–1.5 bar
Typical repair cost £80-160 (including labour)

DIY fix possible

Locate a radiator bleed valve and use a key to release water into a container until the pressure gauge on the boiler drops.Ensure the filling loop valves (usually blue or black levers under the boiler) are closed tightly.Monitor the pressure gauge until it rests between 1.0 and 1.5 bar, then restart the boiler.

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Sime models that show the ALARM 03 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Sime ALARM 03 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026