Was your old boiler a non-combi?
Modern condensing combis I think are designed to be more complex and not last as long. I'm not sure all the complexity and fancy modulation etc is really worth it myself. I'd rather have a boiler that lasts 20 years and that any half-competent gas engineer can fix with a spanner and some spare parts.
£20k, jesus!
Whatever about a combi, you probably don't want a non-condensing boiler these days, not with gas the price that it is.
Old and new both condensing and both non-combi.
Condensing boilers became mandatory in UK just over 20 years ago