I'm really concerned about the safety of the Sonoff devices.
These photos show a TH-16 unit that was fed from a 13amp fused spur (240V) and feeding a 3kW fan heater. Total load was less than 13A, yet this is the second Sonoff that has self-destructed in 4 months. Although there has been a recall for the PCB track tinning, I believe the fault is with the fuse clips. That is where the charring of the board is the worst - the board has literally melted and the fuse bent over to touch the terminal block (by gravity).
What is the rating of the clips? Schurter of Germany make some of the best, and they are only rated at 10amp (http://uk.farnell.com/…/fus…/dp/1453528…)
Until this is sorted I am only running heaters on half power, and am tempted to short out the fuses, as they are protected by a 13A fuse at the spur.