Swapping an old Airtronic for a newer generation Airtronic.

The Airtronic S2 and S3 heaters are fully interchangeable. However, the first-generation Airtronic cannot be directly replaced with a newer-generation heater due to wiring differences.

That said, the dimensions, fittings, and ducting are the same across all Airtronic generations. This means you could replace a first-generation Airtronic with a third-generation model if you also update the wiring.