I bet a pound to a pinch of poop that it was ANGLIAN , Had the same happen to me a while back , south facing house , all the units started to go one by one , no matter what the season they still went , yet the rear windows never broke a sweat HMMMM, LITTLE DODGEY THAT .
My old man has had the same ANGLIAN units in his south facing house for 20 years , 7 of those done by wfp method , still not a single bit of condensation in sight , Anglian cut costs and went for inferior units , simple as that , costs had to be cut cos they ran out of custies , its the same as the roofers these days , nowhere near as much work out there being as the jobs were done a lot better after the storms of 89 , fact from a custie roofer !
Rich