the original valve goes tits up and leaks hot water through on all settings.
have a trawl through the electricals/climate section, ive put some pics of a dead valve in there. it doesnt take a lot of hot water in the matrix to make the cabin warm, the aircon doesnt cool it off under these conditions.

Ive just ordered the bits for a 6th batch, so may be a month or 2 till 7th batch- if you are decidely uncomfortable, I think someone has a standard valve for sale atm on the for sale thread, so this would tide you over for a yaer or two till that one dies.

oh and welcome to exclusivity