Aerolan. The heater in the S1 is quite a simple one there is no adjustment for control from memory. The round knob is just a switch or thats how it seemed to work on mine. The unit looks mechanical to work off elecric a few squirts of WD might be worth lt. Iv'e never seen a car generate so much heat under the bonnet as the S1 did. If you decide to pop the dash back you will have very little space to get at the switch all the cableing is so tight and some very sharp edges. Good luck hope its an easy fix. Em
