Fixing A Neighbour’s Ventilation Unit Cheaply

My neighbour’s Zehnder ventilation unit had stopped working and only showed an error on its display.

The cause turned out to be the sensor that measures outdoor temperature and humidity: it had corroded. Not a board failure, not a control problem — one worn part.

We found a detailed tutorial online, worked through it, and the unit ran again afterwards. A repair well below the cost of calling out a technician.