I have a 12yo John Lewis heat pump dryer. I love it. It is efficient and superb, stops damp air in my house, gets me through wash day with minimal effort, and was a gift to us when our dd was born.
It is broken 
The engineer who came out has checked all constituent parts, but is flummoxed as to why the clothes will not dry. It spins, and it heats, but the water won't come out (i.e. it is not condensing). There is no blockage in any tube/pipe. Could it be something to do with the heat exchanger/coolant? Has anybody had this issue with theirs, and can that be fixed?
We have had this machine repaired twice during its lifetime, and would be happy to continue to repair it, but AIBU? Should we finally give up the ghost and buy a new one? I would hate to see it go, but wondered if anybody here has experience of this sort of fault before we make that decision? I know that 12 years is pretty good going for any appliance, but I hate the thought of scrapping it if it can be avoided.