Hi, if your heating is coming on when you turn on your hot water with this appliance, it is nothing to do with the appliance.
You need to find out if your system is fully pumped - If it is, then you will need to change your 3-way valve... If it is gravity.... Then I suggest you will need to change your anti-gravity valve, or take a look at upgrading your system to fully pumped.
ccMods, July 2006