Hey Graeme.
You said your washer was still under warranty. My advice would be to avoid doing anything that might void the warranty. This would include taking on troubleshooting and repair aspects independently. I would report the continuing problem to the manufacturer (or entity issuing the warranty) and request they honor the terms and conditions stated in the warranty. Whatever the problem turns out to be, your liability and cost, etc., is minimized, this way.
Good Luck.