immersion thermo length

Hi all, i have been asked to change an old immersion thermostat for a new re-settable one. The current one is in an immersion on the top of a cylinder. The problem is the top of the cylinder is only about 12" below the roof and when i withdraw the old stat there isn't enough clearance for it to come out so not sure how long it is. The cylinder is about 4' . I can obviously bend the stat to get it out but putting a new one in will be tricky unless i could use a really short one. Would this drastically affect the performance of the immersion ?
Even taking the cylinder out would be a lengthy job as it has had studded walls built tight up to it on the sides and all pipes and cylinder connections are down the back of it where it is impossible to get to without ripping out a wall.
It has been suggested to me i could bend the new stat to get it in but it would have to have some tight bends to clear the ceiling and then straightened as it slide's into the pocket. Would this not shorten it's life (being polite) ?
Easy option is a short stat but will this be ok ?
Thanks in advance, STIX.

a 27" element will have an 18" stat if it's a 900 x 450 cylinder

What sort of "roof" are we talking?

let the wally who suggested bending it put it in and he can take the blame.
it will knacker it bending it.
a shorter one won't do ever.
if it's in a cupboard cut a small hole in the ceiling.

the roof being the roof of the house. If i cut a hole in the plaster board above the cylinder i'll be looking at laths and roof tiles. Maybe i'll have to go in through the roof.

you only need a hole size of an egg cup. then cover it back over from the loft

No loft, it's one of those where the roof spars have been filled in between with kingspan, plasterboarded and skimmed, so it looks like i'll have to lift a few tiles on the roof to get at it. Thanks for your help, STIX.

have fun. lucky it's not the element then they are 27" long.

You could put a roof window above and open when changing stat?

cut a new side entry 12" immerser, if you are lucky you might be able to leave the old one in (if the new one fits in past it, prob not!!) if you have to remove the old one you won't need to worry how it comes out as it is going in the bin, get a 2 1/4" brass immersor plug to fit in place of the immersor, or i suppose you could remove the old one, cut it down and refit as a plug, but the cost of the plug is probably only £2