I didn’t even need a Big Spanner™ (although I did buy one).
See, after struggling to not even move the existing immersion heater element, I decided to research further. Turns out that task is nigh-on impossible without tearing the copper tank that it’s housed in… so I stopped trying and took a breather.

*Ting!* went the-bulb of inspiration.

‘Why don’t I just change the thermostat bit, seeing as that’s actually the faulty electrical part?’

The therm just slid out of its housing, I slotted the new one in, I replaced the fuse in the fuse-box (which is another subject entirely - I shall elaborate in a mo), switched on and Hoorah! We now have hot water again!

So, if you want to try and track down replacement fuses what are about that long and that round, don’t go to B&Q.
If, like me, you tend to be a little argumentative with unhelpful shop staff, you’ll probably enter into a debate when told to try a smaller electrical shop on the high-street.
The debate will be about why the very existence of B&Q and their ilk means all such little shops have closed ’round here hence your presence in the not-in-anyone’s-opinion-Super Store, in which you cannot buy the fuses you want because that sort of fuse is only available from small electrical shops that have all closed down because B&Q and their ilk exist, who in turn don’t stock fiddling small replacement fuses what are about that long and that round because small electrical shops stock them but such small shops don’t exist any more so you then have to go to somewhere like B&Q and ask if they have any replacement fuses what are about that long and that round but they won’t stock any because AAAAAAAAARGGH!

I can assure you, it’s the sort of ghastly circular topic that can keep going for hours if you find a suitably argumentative staff-member.

And then you’ll probably just buy some regular fuse wire and botch your old fuses up like what I just did.

So, this is what being a Growed Up is all about, eh?

‹Goes for a nice hot bath to try and forget about the horrors that are B&Q Saturday Staff›

‹watches repeatedly›

That’s what the fuse for my immersion heater did yesterday. I didn’t know at the time, of course. I just thought the little light-bulb in the power switch had popped. No, it was only after having a bath today and then attempting to do the washing up that I realised we had no more hot water. None at all. Oh, the joys of Economy 7.

So I checked the fuse, swapped it for another 15A fuse and that went Fzzzzzzzzzzzt too.

It’s of little consolation to know that Immersion Heaters should have a 20A fuse instead of a 15A fuse. A 15A fuse has been fine for at least the last 5 years, so why go Fzzzzzzzzzzzt now?
Bit of a dilemma, really: did the fuse just give out because it’s under-rated for the job, or because there’s a fault with the Immersion Heater? If it’s only under-rated, why did the second fuse immediately go Fzzzzzzzzzzzt? If there’s a proper fault with the heater, how badly is a sparky going to damage our already limited wonga-hoard?

‹Is grateful that the shower has its own water heater›

*By the way, pardon the overuse of the word Fzzzzzzzzzzzt: it was really quite impressive the way the fuse glowed for a moment as it died.