I've seen in searching that someone else had this problem and it's the diverter valve in the heater unit - I've already cleaned the filters, arms, etc and then had the bottom arm replaced as the engineer I called thought it was worn. The machine was better afterwards, but still not as good as it should be.
Dave has confirmed the part I need, and as an ex-BT engineer and now handyman I'm happy to tackle the replacement myself. Looking at the machine, it appears I gain access from the inside, and it looks like the sides have to come off to get in to the bottom.
Can anyone confirm if that's right or not please? Also, is there anything I should watch out for, avoid or whatever? Whereabouts in the machine is the heater unit located so I know where I'm aiming to get?
Thanks for any help you can give,