How long is the heat exchanger warranted on the ZWB 42-3?

The heat exchanger is warranted to remain free of leaks for ten years from the original installation date, provided the boiler is properly maintained by a qualified heating contractor. From year 11 onwards, BTC provides a limited pro-rated warranty where you pay a percentage of the replacement cost based on years of use (20% at year 11 up to 75% at year 15+).