Absolutely correct that any claim would be on ECP as the seller of the plugs however in the first instance given the potential value of the claim contacting NGK direct would register the situation with them. This then adds, hopefully, some weight to the subsequent claim submission to ECP who should be informed that that NGK are expecting the plugs back for inspection. It is vital that phone conversation dates, times and person spoken with are recorded and photos, receipts, signatures, name etc: are obtained when items are handed over to another party.
The fact that the plugs were fitted by a professional and not a DIY person should be advised in the written claim as it demonstrates incorrect fitting can be ruled out as a cause.
