were you the same electrician who wouldn't place a resistor where the N112's are, due to possible complications?
Now that rings a bell somewhere!
Seriously, to the OP,you should try to find out what all "consummers" that fuse feeds, then maybe unplug each of the Lambda probes and try again as the heater shorting out might be marginal and need the extra heat that a "blast" gives it. Uprating fuses, not unknown as a proper fix in the world of VAG - rear wiper motors for instance in Fabia and maybe others of that platform. I can't argue about the fuse being rated to protect the circuit wiring though - that is correct!