I have 520d se E60 2006, with 157K on clock. In January suffered loss of power, went to garage who diagnosed dpf not working due to failed engine thermostat. Replaced and forced regen done. 4/5 weeks later same problem occurred; lamda sensor replaced along with oil and engine filters. Forced regen done again. Same problem occurred yesterday, no warning lights have appeared on either of these occasions to say dpf has problem. RAC call out said error messages recorded included turbo under bust, engine oil thermo sensor and glow plugs 1-4. Have read on various bmw forums that glow plugs/relay can prevent regen from occurring. Is this correct. I know car is high mileage but no problem until this year, vehicle serviced as per computer. Car is with garage who do not seem sure of whats wrong, other than dpf replacement. Any thoughts?