Viessmann Boiler Fault Codes: Complete Troubleshooting Guide

Is your Viessmann boiler displaying a fault code on the control panel? German engineering is known for precision, and Viessmann boilers (such as the Vitodens and Vitopend series) use a sophisticated diagnostic system to tell you exactly what is wrong.

At Termix.ro, we’ve created this comprehensive guide to help you identify Viessmann fault codes, understand their causes, and find the right solutions to restore your home’s comfort.

Common Viessmann Fault Codes and Solutions

Unlike other brands, Viessmann often uses alphanumeric codes (starting with letters like F, E, or B). Here are the most frequent ones encountered by homeowners:

⚠️ Fault Code F2 – Burner Overheating

This occurs when the high-limit safety cut-out has tripped. It usually means the boiler has gotten too hot due to a lack of water flow or a pump failure.

The Fix: Check the system pressure. If it's low, top it up. If the pressure is fine, you may need a technician to check the pump or the heat exchanger.

⚠️ Fault Code F4 – No Flame Signal

The boiler has attempted to ignite but cannot detect a flame. This is common in the Vitodens 100-W and 200-W models.

The Fix: Check if the gas supply is open. Press the Reset button (usually marked with a lightning bolt symbol). If it fails again, the ignition electrode or the gas valve may be faulty.

⚠️ Fault Code F5 – Air Pressure Switch / Fan Fault

This code indicates that the fan is either not running or the air pressure switch hasn't closed, meaning flue gases cannot be safely exhausted.

The Fix: This is a safety issue. Check if the flue terminal (outside) is blocked by debris or ice. If clear, a technician must inspect the internal fan and pressure switch.

⚠️ Fault Code 0b – Low Water Pressure

Similar to "Error 108" in other brands, this means your heating system needs more water.

The Fix: Use the filling loop to increase the pressure to 1.5 bar. The code should disappear once the sensor detects sufficient pressure.

Viessmann Fault Code Reference Table

Fault Code	Description	Recommended Action
F1	Flue gas temperature limit exceeded	Check for scale in heat exchanger
F8	Fuel valve closes too late	Requires professional service
FC	Fan control / Fan speed too low	Check fan and wiring
EE / EF	Flame signal fault during start-up	Check ignition leads and electrodes
A7	Control unit fault	Restart boiler; if persistent, call service
B7	Boiler encoding plug fault	Requires technician intervention

10 Constant operation. Short circuit to outdoor temperature sensor. Check the outside temperature sensor and cable.
18 Constant operation. Interruption to the outdoor temperature sensor. Check the outside temperature sensor and cable.
30 Burner blocked. Short circuit to boiler temperature sensor. Check the boiler temperature sensor.
38 Burner blocked. Interruption to the boiler temperature sensor. Check the boiler temperature sensor.
50 No domestic hot water is prepared. Short circuit to the domestic hot water temperature sensor in the battery. Check the sensor.
51 No domestic hot water is prepared. Short circuit to the temperature sensor a.c.m. at the exit. Check the sensor.
52 Burner blocked. Volumetric flow sensor short circuit. Check the connections and the cable, replace the sensor if necessary.
58 No domestic hot water is prepared. Interruption to the boiler water temperature sensor. Check the sensor.
59 Do not prepare domestic hot water. Interruption to a.c.m. at the exit. Check the sensor.
5A Burner blocked. Volumetric flow sensor interruption. Check the connections and the cable, replace the sensor if necessary.
A0 Burner blocked Dynamic gas supply pressure too low. Checking the gas pressure and the gas pressure switch.
A3 Burner blocked. The flue gas temperature sensor is not positioned correctly. Install the flue gas temperature sensor correctly.
A9 Controlled automation operation without the influence of an Open Therm unit. Communication error on Open Therm unit. Check the connections and cable, replace the Open Therm unit if necessary.
b0 Burner blocked Short circuit at the flue gas temperature sensor. Check the sensor.
b7 Emergency mode. Ignition error. Disconnect the on-off switch and reconnect.
b8 Burner blocked. Interruption to flue gas temperature sensor. Check the sensor.
0A Burner blocked. Dynamic supply pressure too low. Check gas pressure and gas pressure switch.
0C Burner blocked. The mains voltage is too low. Check the mains supply.
E3 Burner on failure. Error in the circuit of safety elements. Check the temperature limiter and connecting cables.
E5 Burner blocked. Internal error Check ionization electrode and connecting cables.

F0 Burner blocked. Internal error Automation is being replaced.
F1 Burner on damage. Max. of flue gas has been exceeded. Check the filling level of the system. Check the circulation pump. Ventilate the installation.
F2 Burner on damage. Temperature limiter disconnected. Check the filling level of the installation. Check the circulation pump. Ventilate the installation, check the temperature limiter and the connection cables. To unlock the burner, turn the "vitopend 100 wh1d fault indicator" button briefly to the limit to your right and then back (Reset).
F3 Burner on damage. There is already a flame signal when the burner is started. Check the ionization electrode and the connecting cable. Disconnects and reconnects the on-off (or reset) switch.
F4 Burner on damage. There is no flame signal. Check the ignition / ionization electrode and the connecting cable, check the gas pressure, check the valve block, ignition and ignition mode. Disconnects and reconnects the on-off (or reset) switch.
F5 Automatic ignition on failure. The air switch is not open when the burner is started or does not close when the ignition speed is reached. Check the exhaust / air intake system, the hose from the pneumatic switch, the pneumatic switch and the connecting cables. Disconnects and reconnects the on-off (or reset) switch.
F8 Emergency burner. The fuel valve closes late. Check the valve block. Check the two control paths. "Reset" is performed.
F9 Emergency burner. The blower speed when starting the burner is too low. Check blower, blower connection cables, blower power supply, blower control. "Reset" is performed.
F30 Burner blocked. Short circuit to boiler temperature sensor. Check the boiler temperature sensor.
F38 Burner blocked. Interruption to the boiler temperature sensor. Check the boiler temperature sensor.
F50 Do not prepare domestic hot water. Short circuit to the domestic hot water temperature sensor in the battery (only for the wall-mounted gas heating boiler). Check the sensor.
F51 Do not prepare domestic hot water. Short circuit at the outlet temperature sensor (boiler for heating and cooking a.c.m on gas). Check the sensor.
F58 Do not prepare domestic hot water. Interruption to the domestic hot water temperature sensor in the battery (wall-mounted boiler for gas heating). Check the sensor.
F59 Do not prepare domestic hot water. Interruption to the sensor for the outlet temperature (boiler for heating and cooking a.c.m on gas). Check the sensor.
FA Burner on damage. The blower stop point has not been reached. Check blower, blower connection cables, blower power supply, blower control. "Reset" is performed.
FC Burner blocked. Blown electrical control (automation) defective. Check the connection cable to the blower, check the blower, possibly replace or replace the automation.
Fd Burner blocked. Ignition error. Ignition electrodes and connecting cables are checked. Check for a strong disturbing field (EMC) near the unit. "Reset" is performed. If the fault is not repaired, the automation is replaced.
FF Burner blocked. Ignition error. Ignition electrodes and connecting cables are checked. Check for a strong disturbing field (EMC) near the unit. "Reset" is performed. If the fault is not repaired, the automation is replaced.
–– (lightning) Burner blocked Communication error between ignition control and control unit Checking the connection cable. "Reset" is performed. If the disturbance is not remedied, replace the ignition switch or the control unit.

When to Call a Viessmann Specialist?

If your boiler requires a Reset more than once, it is a sign of an underlying issue. While topping up the water pressure is a DIY task, any internal repairs to the burner, gas train, or heat exchanger must be handled by a Gas Safe registered engineer.

Need Viessmann spare parts or a new Vitodens installation? The Termix team provides expert advice and high-quality heating components to ensure your Viessmann system operates at peak efficiency.