No your heating loop that supplies your radiators should be filled using unsoftened water and treated with a suitable and approved inhibitor. This process is easily achieved by using the water softener bypass which should always be fitted as part the WS455’s installation. We recommend reading the WRAS Information and guidance note No 9-07-01 Issue 1 “Information for Installation of Ion Exchange Water Softeners for Systems Supplying Water for Domestic Purposes” for more information.