2002 mercedes s500 trunk will not open

Hi there
First of all may i say i feel your pain. literally. the same thing happened to mine. here is what i did
Firstly i needed into a locked boot urgently (for wifes wheelchair)
so i cut a rectangle out of the boot put my hand in and pulled the release mechanism, that worked but left me with a hole in my boot.
I suggest that you try this instead.
remove back seat
the central locking pump is located next to the battery (black box with yellow air lines going into it.)
Unplugg the filler cap cover air line, then unplugg the boot air line and put it into the filler cap cover socket.
now when you unlock the car the boot should automatically open.
If it does not the problem it on the boot air line and you should strip the trim out of the boot to check, but you still have to get in and may have to do what i did initially.
If changing the air line worked then you will soon get tired of having to shut the boot everytime i solved this problem by routing the filler cap air line to a pnuematic switch (LEGO) This switches between the boot and the filler cap. bit naff but it works and cheaper than having to replace pump and have computer and keys re-coded total cost around £600.
op that helps