On 24/04/2018 11:36, 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?

Is the compressor definitely running not just the fan?

I had a "posh" Misubishi one that stopped working a few years back but
fan was working. Finally last autumn I thought "kill or cure" and
dismantled the beast. Fortunately before I did too much destructive
investigation I spotted a bulge in a large square packaged electrolytic
capacitor. Couldn't find an exact 450V(?) match but found a similar one
at 350V from RS. bought 2, fitted one and it's been working perfectly
since then, plus I now have a spare capaitor stored inside the unit for
when it's required in the future.