Hola. Ever since we moved into our house 5 years ago we've complained about the upstairs not being warm enough, but have always been happy with the temperature downstairs. Strangely of late the downstairs seems to be colder and the upstairs a little warmer than before. We have a combination boiler and the radiators are newish (4 years). My wife assures me she has not messed around with the thermosatat and TRV's. The house is better insulated downstairs and we've not changed anything so this really doesn't make any sense. Can anyone explain this? I thank you

has the system been balanced properly.
no good adjusting trv's when the systems out of balance.

also we know very little on your system.
where is the boiler ?
wheres the first radiator, last radiator, upstairs, downstairs etc ?