What does fault code 18 mean on Viessmann Boiler?
- SSabrina McclainSep 13, 2025
Fault code 18 on your Viessmann Boiler indicates a lead break in the outside temperature sensor. Check the outside temperature sensor and lead.




What does fault code 18 mean on Viessmann Boiler?
Fault code 18 on your Viessmann Boiler indicates a lead break in the outside temperature sensor. Check the outside temperature sensor and lead.
What to do if my Viessmann Boiler shows fault F4?
If your Viessmann Boiler displays fault code F4 and there's no flame signal, you should inspect the ignition/ionisation electrode and its connecting cables. Also, verify the gas pressure, gas train, ignition components, ignition module, and ensure the condensate drain is clear.
How to fix fault F2 on Viessmann VITODENS 050-W?
If your Viessmann Boiler is showing fault code F2, which indicates the temperature limiter has responded, you should: 1. Check the heating system fill level. 2. Check the circulation pump. 3. Vent the system. 4. Check the temperature limiter and connecting cables.
How to solve Viessmann VITODENS 050-W Boiler control unit not increasing set value?
To address the issue of the control unit not increasing the set value on your Viessmann Boiler, increase the set value and ensure heat is drawn off.
How to solve control unit issues with no increase set value on Viessmann VITODENS 050-W Boiler?
To address control unit issues with no increase in set value on your Viessmann Boiler, increase the set value and ensure that heat is being drawn off.
Why Viessmann Boiler has no DHW heating with error code 51?
If your Viessmann Boiler is not heating domestic hot water (DHW) and showing error code 51, it could be due to a short circuit in the outlet temperature sensor. Check the sensor (see page 66).
What does fault E5 mean on a Viessmann Boiler?
If your Viessmann Boiler displays fault code E5, indicating an internal fault, you should check the ionisation electrode and the connecting cables.
What does fault F5 mean on Viessmann VITODENS 050-W Boiler?
If your Viessmann Boiler displays fault code F5, indicating an internal fault, you should check the ignition electrodes and connecting cables.
What to do if Viessmann VITODENS 050-W fan doesn't start?
If the fan in your Viessmann Boiler doesn't start after approximately [ ], check the fan, fan connecting cables, fan power supply, and fan control.
How to resolve fault 52 on Viessmann VITODENS 050-W Boiler?
If your Viessmann Boiler displays fault code 52, which indicates a short circuit in the flow sensor, you should check the connections and lead. If necessary, replace the sensor.
Essential safety guidelines to prevent accidents and material losses.
Explanation of danger, warning, and note symbols used in the manual.
Safety rules for connecting and operating the appliance, including contractor requirements.
Guidelines for safe interaction with the appliance during use and maintenance.
Information on system commissioning and the appliance's intended applications.
Definitions of terms and details about the system's preset factory configurations.
Advice on how to optimize energy consumption for heating and hot water.
Identification of display and control elements on the appliance.
Explanation of symbols and basic operation using the control interface.
Details on operating modes like controller-based and weather-compensated.
Step-by-step guide for safely starting the heating system.
Instructions for safely shutting down the entire heating system.
Specific procedures for shutting down central heating and domestic hot water.
Adjusting heating water and boiler water temperatures for central heating.
Setting room temperature based on outside conditions.
Procedure for adjusting the temperature of domestic hot water.
How to initiate the test mode for flue gas inspection.
Procedure for terminating the emissions test mode.
Causes and remedies for insufficient room heating.
Causes and remedies for excessive room heating.
Troubleshooting steps for hot water supply problems.
Guidelines for cleaning the appliance and its regular maintenance.
Maintenance recommendations for the boiler and safety notes for the power cable.
Definitions of technical terms used throughout the manual.
Essential safety guidelines to prevent accidents and material losses.
Explanation of danger, warning, and note symbols used in the manual.
Safety rules for connecting and operating the appliance, including contractor requirements.
Guidelines for safe interaction with the appliance during use and maintenance.
Information on system commissioning and the appliance's intended applications.
Definitions of terms and details about the system's preset factory configurations.
Advice on how to optimize energy consumption for heating and hot water.
Identification of display and control elements on the appliance.
Explanation of symbols and basic operation using the control interface.
Details on operating modes like controller-based and weather-compensated.
Step-by-step guide for safely starting the heating system.
Instructions for safely shutting down the entire heating system.
Specific procedures for shutting down central heating and domestic hot water.
Adjusting heating water and boiler water temperatures for central heating.
Setting room temperature based on outside conditions.
Procedure for adjusting the temperature of domestic hot water.
How to initiate the test mode for flue gas inspection.
Procedure for terminating the emissions test mode.
Causes and remedies for insufficient room heating.
Causes and remedies for excessive room heating.
Troubleshooting steps for hot water supply problems.
Guidelines for cleaning the appliance and its regular maintenance.
Maintenance recommendations for the boiler and safety notes for the power cable.
Definitions of technical terms used throughout the manual.
| Model | VITODENS 050-W |
|---|---|
| Category | Boiler |
| Energy Efficiency Class | A |
| Max Working Pressure | 3 bar |
| Electrical Connection | 230 V / 50 Hz |
| Type | Wall-mounted |
| Fuel Type | Natural gas/LPG |
| Dimensions | 700 x 400 x 300 mm (H x W x D) |
| Connection for Heating Flow/Return | 3/4 inch |
| Connection for Gas | 1/2" |
| NOx Emissions | Class 5 |











