Spot on I expect in the UK the IRD is heated by coolant rather than the other way round!!This is the first time I've heard of such a problem.
As you suggest it's probably an internal fault in the cooler.
The drive train set up is designed to be suitable for climates from the Arctic Circle to the Sahara Desert so I would reckon that an IRD in the UK would manage fine without being cooled at all over the winter.
Singvogel.