Viessmann Vitodens 111-W Error 91: Function of affected extension in emergency mode

Viessmann Vitodens 111-W water heater · taken from the manufacturer’s manual, pages cited

Fault code91

Fault 91 indicates the function of an affected extension is in emergency mode due to a DIO electronics module communication error. The manual's first action is: “Check connections to DIO electronics module and connection to HBMU heat management unit.”

Model
Viessmann Vitodens 111-W
Display shows
Function of affected extension in emergency mode (91)
Type
Fault code
Source
Manual p. 71

What 91 means

Function of affected extension in emergency mode p. 71

Common causes

  • DIO electronics module communication error p. 71

What to do

  1. Check connections to DIO electronics module and connection to HBMU heat management unit. p. 71

If 91 is still not resolved

The manual gives no further instruction for this code. Open the code table in the PDF or contact Viessmann service.

Open the manual at page 71 All Vitodens 111-W error codes Manual details & download

This page summarises what the manufacturer’s manual says about 91; each statement links to the page it comes from, and quoted lines are copied word for word. It is not a substitute for the manual or for a qualified installer. ManualLib is not affiliated with Viessmann. Found a mistake? Report an error.