Having worked over the years on a good hundred or so I'd hope I have seen the best and worst.
I'm yet to see one in situ that's older than 5years, by that time it's normally been ripped out and replaced.
Common sights are continual E4, E5 faults, dodgy rope seals, gaskets, probes, drifting gas valves, PCB boards that don't last a year.
Not seen a single one yet where the flex tube on the condense syphon hasn't gone brittle with big holes in due to its location and the fact that it's design means it touches one of the CH pipes.
Front covers all warp.
Bottom left of boiler always rots through from inside to out.
Passing divertor valves,leaking pumps and pressure gauges that don't read
They are absolute garbage, it used to be that you had to order parts by serial number of boiler, now one of the independents that pushed the avanta hard, carry all available spares and just dish them out when you ask without any serial numbers.
There isn't a day goes by where people
Aren't in there getting soared for dodgy avanta's.
I'll be ripping 2 out in a couple of weeks that remeha commissioned, will be 5 years old when they come out and remeha voided their own warrenty after 12months because of the amount of visits they were making.
Good luck with yours DH, you'll need it.