Lobster wrote:
I've got a dehumidifier, a few years old now. Recently I've been
getting the 'defrost' warning light on all the time, supposedly
indicating that either the ambient tempoerature is too low (it isn't)
or that the air filter is clogged (it isn't).

The fan and compressor run apparently normally, but the unit is no
longer collecting any significant amount of water. I've opened up
the unit while running, and it's copper cooling coils feel about room
temperature.

The model is a B&Q-branded WDH-610HA (see
https://www.amazon.co.uk/dp/B00AFCMTXO)

Any ideas what's wrong, please, and if it's fixable?

Thanks

The coils should be very very cold. A wet finger should stick to them.
It has a leak and lost the refrigerant.
Not worth repairing. Sorry.