Bmw e91 2007 dpf filter wont do regen

[Frank e91]

Hi having problem with e91 not doing regen.
Have replaced thermostats as were stuck open.
Have replaced glow plugs and control unit.
There are no fault codes apart from dpf filter is partially full.
Have driven with fault code reader plugged in it says it's trying to do a regen but then stops and keeps turning on off. Any ideas would help thanks