Heat bed too hot

[bzhmaddog 0]

Hi guys. I recently purchased a Prusa i3 (custom acrylic frame). It is printing really well but I have a weird issue with my heatbed (PCB Heatbed MKII).

My problem is whatever value I set in Cura for the bed temp (70°C for instance since use PLA) the Heatbed always goes higher than the limit. It usually stabilise at ~90°C and even when I tune the temp from the LCD panel it keeps the temperature higher.

For small prints it is not really an issue since the print is finished before the temperature gets at its highest point but for larger prints it affects the first layers (they melt together and bend).

Any idea what could cause this ?

The firmware loaded in the board is Marlin 1.0.0 RC-2-mm and I am using the latest Version of Cura with the i3 profile available (just tweaked the filament size).

Thx in advance for you help/advises.