Taking an axe to an electric box that shuts off power would not make temperature rise in the sauna.
Coroners do not make photo enlargements of CCTV shots. They pass the job on to police photo lab technicians.
The events of the episode are said by numerous characters to take place just before Halloween, yet when Fleur Perkins shows Barnaby and Winter her tablet with photos of the bootprints, the date says Wed 4 Nov. This could be the actual date the scene was filmed as filming took place in October and November 2020.