Power not supplied to heated bed

I have a Prusa i3 Hephestos, and attempting to add a heated bed to it as the original kit I bought didn't include it.

I've wired up the heated bed and thermistor to my Arduino, as well as set #define TEMP_SENSOR_BED to 1 in the firmware then successfully loaded it. This has got to the state where when I try a print, the display correctly shows the current temperature of the bed from the thermistor, the target temperature as well as "Bed heating". The print won't start until the bed reaches the required temperature.

However, no power is supplied to the D8 position which is where the heated bed is attached.

Has anyone else had this problem?

Thanks.

Bad MOSFET maybe? Have you checked D8 for 12v? Does the led light up?

I stuck a volt meter and couldn't get a reading. I don't have an LED though, so can't tell if it lights up. Is there any way to replace the MOSFET without changing the whole board?

Silly questions first...
Have you got 12v power from the PS connected to both of the power input sockets on the Ramps?

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Waitaki 3D Printer

Ah.

I haven't, didn't even know that was a thing. Thank you very much, will try it and get back to you!

Yup that was the issue, no further input is needed.

Thanks for the replies