Just a thought,

When washing it, you haven't dislodged something that has maybe fell onto the header pipes ? A washer, Key ring fob, piece of tape ???

I'd start (in any of the cases) by looking for the evidence of a burn, the header pipe and work my way back - if you find nothing then as Jenny says it's maybe a short somewhere ?? Dare I say the rectifier ????

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Never underestimate the power of stupid people in large groups.