Just had the boiler condemned in one of our rentals, it's an oldish boiler and they've said the repairs will be getting towards £500 depending what they find when it's taken apart, ( emissions are sky high, plus expansion vessel leaking etc etc ).
A new boiler is probably going to make more sense going forward.
It's a standard 3 bed semi, not massive, typical of what you'd find on a modern estate, what ball park figure should I be expecting, ( so as my pants are not pulled down too far, lol ).