Viessmann Boiler Error Codes — Complete Guide

Both F2 and EA indicate the Viessmann boiler has failed to establish or maintain a flame. These are among the most common Viessmann fault codes.

Initial checks:

1. Check gas supply — does the hob work normally?
2. If no gas anywhere — call National Gas Emergency: 0800 111 999
3. Press Reset once and monitor for 10 minutes
4. If the code returns — call FE Maintenance

If gas supply is fine, likely causes include:

• Dirty or worn ignition electrodes
• Faulty ionisation / flame detection rod
• Gas valve not opening fully or consistently
• Low gas pressure at the meter
• PCB failure

F4 indicates a fault with the flue gas temperature sensor. This sensor monitors the temperature of gases leaving the boiler through the flue.

When the sensor fails or reads an incorrect temperature, the boiler locks out as a safety measure to prevent overheating or dangerous flue gas temperatures.

This fault always requires a Gas Safe engineer. Possible causes:

• Failed temperature sensor (most common)
• Wiring fault to the sensor
• Actual flue gas temperature problem (blocked or shared flue)
• PCB fault

0E (displayed as OE on some models) indicates a fault with the flow temperature sensor — the component that measures the temperature of water leaving the boiler into the heating system.

Without accurate flow temperature readings, the boiler cannot control its output safely and locks out.

Typical causes:

• Flow temperature sensor (NTC thermistor) failure
• Sensor connection/wiring fault
• Actual water temperature issue (pump failure causing overheating)

Viessmann is a premium German boiler brand. Parts are often more expensive than budget brands but the boilers are built to last 20+ years with proper maintenance.