Trouble with SSR @ D8: Heatbed never turning off (3 replies)

Hi there,

I've connected a 24V PSU controlled by RAMPS 1.4 (D8) via SSR to heat the printbed.
While heating up works (kinda) it seems that the Marlin firmware doesn't turn off D8 after reaching target temperature - nor does it if the target temperature has been decreased (for later layer).
The SSR keeps permanently routing power to the heatbed which temperature gets higher and higher, causing warping and so on.

I took the heatbed off (Pronterface) and measured still around 4V on D8.. this may be a side effect by the powered SSR.. and may be this causes the heatbed to 'overheat'?
Its a chinese SSR, input: 3-32V , output: 5-110V single phase DC/DC - well cooled by a CPU cooler ;)

Any help?
The uncontrollable heatbed causes warping and makes it impossible to print larger parts :/

thanks!