I was fishing out some info on the net on the techniques for removing an immersion heater. Colin Lloyd is this weekend swapping over from Direct Flow to indirect, by fitting a reto coil into his top-mounted immersion socket. Word is this can sometimes be tricky if the previous plumber has used boss white.
The following is the best collection of tips and techniques on removing a stubborn immersion that i could find! Thought it'd be worth sharing..