best one is to follow what garage mechanics do when the van is serviced - suck noisily through teeth before telling customer that its jammed in and is likely to crease cylinder when removing immersion. then appply club hammer to immersion spanner three times v hard, if all goes well, replace immersion, if spanner turns along with immersion along with top of cylinder revert to plan B, install new cylinder and smile at higher profit margins you achieve on cyl swap compared to immersion swap. lifes hard but why go to the hassle of stiching and heating when you are more likely to set fire to the towels in the airing cupboard than get the bloomin immersion out without causing problems with swarf etc. Dont forget, you all out there trying to earn a living, you can try to hard if your not careful.