Hello
I have one of these and for a change the problem is not with the care filter.
To get the machine to work you have to hold the on button in. You normally press the button, machine starts and then you can release it
Am i being optimistic here hoping that all I need to replace is the on/off switch??
The on/off switch is a non-latching one, so the fault will almost certainly be the relay board. Check for dry solder joints, if nothing is visible you can safely assume that the relay is at fault.