Viessmann F5 Fault Code: What It Means on Older Vitodens 100-W Boilers
Estimated reading time: 3 minutes
A Viessmann F5 fault code on an older Vitodens 100-W boiler usually relates to the boiler’s air-pressure and flue safety checks. The boiler may lock out when it cannot confirm the correct conditions for safe operation.
This guide is for older Vitodens 100-W boilers only. Viessmann fault-code meanings can differ between boiler models, so always check the manual for your exact appliance.
Quick Answer
The F5 code can be linked to the air pressure switch, the flue system, fan wiring or the fan itself. Do not remove the boiler case or attempt to repair internal components. You can follow your boiler manual to reset it once, but if F5 returns, contact a Gas Safe registered engineer.
Table of contents
What Can Cause a Viessmann F5 Fault?
On older Vitodens 100-W boilers, an engineer may need to investigate:
A fault with the differential air pressure switch
A problem affecting the flue-gas system
Loose, damaged or faulty fan wiring or plug-in connections
A fan or blower fault
A power-supply issue affecting the fan
The F5 code does not confirm that one particular part has failed. Proper diagnosis is needed before ordering a replacement.
Safe Checks for Homeowners
Check the exact boiler model and note the full fault code shown on the display.
Use the reset procedure in your boiler manual only once. Reset controls differ between Viessmann models, so do not guess the reset process.
Do not remove the boiler casing, touch internal wiring or attempt to dismantle the flue. Do not block, cover or alter the flue terminal.
When to Call a Gas Safe Engineer
Call a Gas Safe registered engineer if:
The F5 fault code returns after a reset
The boiler does not restart
You can see an issue around the flue terminal
You are unsure whether your boiler is an older Vitodens 100-W model
An engineer can check the flue system, air pressure switch circuit, fan connections and fan operation safely.
FAQs
You can follow the reset instructions in your boiler manual once. If the F5 code returns, the fault needs professional diagnosis.
No. The fan is one possible area for an engineer to check, but F5 can also be linked to the air pressure switch, wiring or flue system.
No. This fault involves boiler safety and combustion-related components. It should be diagnosed and repaired by a Gas Safe registered engineer.
No. Fault-code meanings can vary between Viessmann boiler models and generations.
Key Takeaways
- The Viessmann F5 Fault Code usually indicates issues with air pressure and flue safety on older Vitodens 100-W boilers.
- Possible causes include faults with the air pressure switch, flue-gas system, fan wiring, or a power supply issue.
- Homeowners should only reset the boiler once and avoid tampering with internal components or the flue system.
- If the F5 code persists after resetting, contact a Gas Safe registered engineer for proper diagnosis and repairs.
- F5 meanings can vary by model, so always refer to the specific boiler manual for accurate information.
