Mathew Newton was thinking very hard :
That's not good to hear, but good to know - thanks!

It might be worth your while if you intend to keep the boiler a while,
to take those cables out and replace the centre section with heat
resistant wires. Its a short loom, of four or five wires, which unplugs
at each end. Just snip close to the plugs, then solder in and sleeve
heat resistant wires. I suspect that cable failing, might be the cause
of the transformer burning out..