Overheating internal shower cabling

Hi All,
Hopefully someone can help me with this problem:
I've got a Gainsborough Energy1000x shower that started smoking today with the usual acrid smell of burning plastic. After isolating from the supply (and after getting dried off ;-) , I popped the cover and found that the overheating had actually been taking place at a terminal block, where the mains comes in and branches to the heater and other places. The terminal block is the most common type, like the ones in this image:
http://www.maplin.co.uk/media/largeimages/1153i0.jpg . I'm guessing it's a 30A one, due to it's size (and function).
Other than the overheating (which re-occurs after 5-10 mins of use), the shower is fine and the water temperature is normal. Is it possible that the only problem here could be the terminal block itself? The wires are fine, albeit a little blackened near the block. They don't feel overly warm while the shower is running, even when the overheating of the block is becoming evident. No other signs of overheating can be seen elsewhere. With the shower in a moist environment, could it be perhaps that the terminal block has corroded and now has enough resistance across it to heat it up beyond what it can handle?
I've got home insurance that'll cover a repair, but they estimate a 3-week turnaround in the claim, meaning I have to go without showers. I'd rather fix this myself quickly than smell bad!! A local repair tradesman suggested that the brand were prone to overheating, but he also wanted to fit a new one, so that has to be taken with the usual pinch of salt.
If it were likely to be the terminal block, would changing the affected wiring also be neccessary? As I said before, they are a little charred, but the insultion seems fine. I don't have crimp tools (for the other end), so making replacement wiring would be difficult.
Thanks in advance for any pointers!
Fraser.
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Speedy indeed, cheers for the rapid response!
I don't think the plastic insulator itself has become conductive, I'm thinking more along the lines of where the wire mates with the terminal screw and conductor. If the surface of the two metals were to corrode, I'm guessing that the resistance of the terminal will essentially increase, which would increase the amount of heat it generates. But my physics are a little rusty, hence my uncertancy.
As the shower has been fine for several years, I'm really stuck for suggestions on what exactly has changed to make this basic part overheat all of a sudden. The local weather is abnormally warm here at the moment, and the water from the storage tank is also warmer than normal, so it's not as if the shower is working extra hard at the moment. Other than the terminal overheating, it seems fine.
Before posting, I googled some and found suggestions that household showers can also creep up on how many amps are being used, over years of use. This is the only other suggestion I have to why the terminal block is overheating. However, to check this out, I'd need to hook my DVM up in series with a live 30A circuit that has by definition running water very very close by. I'm gonna check the alternatives out first I think...!!

Yeah, I was thinking something along those lines, perhaps creating a loop between both sides of the terminal, with 30A cable. Replacing the terminal block isn't a big deal either, it's cheap stuff and a ten minute job. I'd rather not do it though, if it's unlikely to fix it, because if I do need to get a professional in, they'll complain about my DIY antics, which might mess up the home insurance.
Fraser.
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