I have just come across this question (7th December 2020), so a bit late for this questioner. However, there might be others who have the same problem.
I have found the RMG 25 oil filled a great heater, and mine also just stoped working. When I removed the front cover, which contains the elecrics, I found the on/off switch had failed. No Dimplex spares available, so bought another rocker switch and mounted into the cover - now works!