The air flex machain u have if you phone up tony they sell a probable heater ,which I bought same time as mini arflex two main resons minne light for going up straits lightest in it class , and the inline heater for instance hot water as I do lots of letting agents work whom never have hot water ,or combine boiler broken down , great peace of kit , my mate just bought one ,it was about £100 cheaper than the one from tony but doesn't hate up water as quick , and a regular flow of hot water