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I've got a random f4 fault on a 330+. From start boiler lights up runs to temp all good. Turn the clock off then back on, boiler doesn't go through sequence just go's straight to f4. Reset boiler and can do the same, eventually relight. All checks have been completed. New parts fitted as follows, heat ex, gas valve electrodes, harness. Also a pcb but not by myself. All the parts were new dead stock, free (the only reason I'm trying) Any ideas, it's a qercky one?