How to access heater on Miele T454?

Our Miele Novotronic T454 tumbler drier is no longer providing any heat. I have opened up the front (whole front hinged on rhs) & checked that the heater relay K1 is working ok & there is a supply to the heater which must be somewhere behind the drum, but i can't see how to gain access.
I have removed the 6 m5 hex head bolts from the circular plate at the rear of inside the drum, but the plate won't come away.
Any ideas on how i access the heater & thermostats?