It was not the train manufacturer, but a body shop (Swoboda Karosserie- und Stahlbau GesmbH, now Carvatech), which was recruited by the Gletscherbahn Kaprun (GBK) for renovations. It might have not had so large repercussions if anyone of the actors during those renovations had done his job correctly tho:

• the model chosen was for household use and chosen because the recommended fan heater was unavailable
• other departments of Swoboda (and because of that, everyone else) were not informed about this change, even leading to sending out the documentation of the recommended fan heater to GBK
• the fan heater was mounted in a way that allowed liquids to leak inside of it
• it was mounted directly in front of the hydraulics, which contained flammable liquids
• those hydraulics were redone during the renovations by Mannesmann-Rexroth AG (now Bosch Rexroth AG), and were done using plastic pipes and were not appropriately encased.
• They started melting because of the malfunctioning heater, spraying flammable oil at 190 bar into the fire
• the dropping oil pressure caused the train to automatically break
• but the hydraulics were also needed to open the goddamn doors.

On top of all that, because the cable cars were made of aluminium, they were deemed inflammable. This did not take into account that any installed equipment or passengers and their luggage might NOT be fireproof.

This lead to: no fire exits, no emergency signage, no training for employees how to react in case of fire.

it was a single malfunctioning heater, but the Kaprun disaster had many fathers.

I found a nice paper regarding the different actors written by a student of the University of Virginia here, well sourced.