Doubles the price of smaller low priced units. Two W-B Juniors can be had
for around £1,000 and will deliver approx 20 litres/min. Look around for
a
20 l/min combi and see what the prices are.

Or you could just keep the existing system and spend 500 quid on a single
boiler, forget all the combi nonsense (with attendent expensive/time
consuming replumbing) and have 80 litres/min.

Christian.