Two months is an odd (and short) period to give a warranty. I expect it was more than just a bit of wiring renewed for £300 (unless they were seriously ripping you off). Wires don't burn without cause and that cause has to be excessive current caused by either a faulty component or damage to cabling (shorting wires together), so one has to wonder whether they actually found and fixed the root cause (and suspect they didn't if similar symptoms have recurred).
I would suggest going to Citizens Advice as soon as possible. I think consumer law (Supply of Goods and Services) says the repairs have to be done to a reasonable standard and last for a reasonable period of time (the law doesn't say what "reasonable" is - that's up for debate but I would say more than two months, more like 12 months for that sort of repair). The point is that consumer law trumps warranties. In fact warranties are just icing on the cake of consumer law. As I said, act without delay.
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