Indesit IS70CS Condenser Dryer not heating properly?

Machine is an IS70CS, NOT the IS70C. Replaced the rear heating unit (with the 4 elements and 2 thermostats) after old one died. Drum gets barely warm. Washing load took 6hrs to dry. Machine feels very warm to touch at the back so there's obviously heat but it's not getting through to the drum. The thermostats aren't the type with a reset hole so I know it isn't those. Help!