Lobster brought next idea :
I have a portable dehumidifier (Wickes own brand; I think it's a compressor
model?) about 18 months old which has stopped working.

The humidistat appears to be working in that if you turn it up, it clicks in
and the dehumidifer motor starts working; however the water output container
remains bone-dry.

Any thoughts as to what might be wrong, and whether it's repairable or a bin
job?

A compressor type has a motor and you suggest a motor starts -so it is
indeed a compressor type. One more check you could do is on the cooled
matrix which should quickly become cold when the motor runs. If it is
not getting cold, then it has lost its gas. If it is only 18 months
old, then take it back and quote the Sale of Goods act to the supplier.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk