They were bought in March and July 2011
Yes, but the reason for that is they've probably not been used since October 2013. Both failed to retune when retuning all the tvs.
All the tvs in the house are on a "system". One of the non-tuning tvs has been moved to an aerial socket which is known to work.
One point is that the 3rd working tv appears to have a software setup identical to a manual I have downloaded - a Toshiba manual for the model no - whereas the 2 non-working ones appear to be different but identical to each other.
Sorry, yes, they are all on the same aerial which is fed to an amplifier which then distributes the signal. What I will now do, is move a working tv onto a connection used by a non-working tv and see if that works ok. That should then eliminate aerial issies.
The identical working tv was moved to the aerial socket used by one of the non-tuning tvs, and it works fine, performing an autotune scan as I would expect. By "Air", I presume you mean analogue. These are digital tvs anyway so there should be no need for any converter and, as I say, there is one working perfectly, bought at the same time.and it has not been modified in any way.
Non working tv moved to known working socket - tv still not working.
Working tv moved to location of non-working tv - tv still works.I don't think aerial sockets are the issue.
The failure at the same time cannot be assumed - simply that they were turned on together for the first time in a long time. By that I mean that they were not connected to a mains supply. I have also remembered, that one had not been connected to the aerial since July/August 2013. The autotune goes through the motions of scanning for a signal but doesn't find anything.
I'm ok to do a repair myself but a) what is parts cost likely to be and b) how quickly can they be obtained. In this context time is important.