Ideal Icos HE24 Problems -Worried!?

Hello, I've recently changed the PCB & thermistor in a Ideal Icos HE24 after lots of error codes ie overheat/thermistor/ failed to light. After 1 week the wiring loom has burnt out - is this just bad luck or a fault somewhere? The boiler worked great for the full week until the heating was left on for about 6 hours. I have ordered a new loom but am worried about fitting it incase there is an underlying problem.