Washing machine will not spin heavy bedding after multiple engineer visits

[user1471505356]

My washing machine after 18 months will not spin with a heavy duvet cover just turns slowly aimlessly, a light load no problem, have had 6 engineers visits.

I have a Bosch serie 6, it's not over keen on unbalanced loads. If I'm doing towels or bath mats I usually put it on the lowest possible spin speed, let the cycle run then do an additional normal speed spin after. Usually does the trick. The washer repair man suggested doing this to help the machine last longer.