Heating Repair

1. First of all I would make sure that the problem is with the thermostat. If there was work done on the building and/or heating system were the radiators purged afterwards? It is possible that the radiator is filled with air and not hot water. There should be a small screw on the top of each radiator for purging. Open this screw a small amount. If air comes out keep the screw open until water starts to come out and then close it. Do this with each radiator.
2. If thermostats are infrequently opened or closed (or always left on the same setting) the valve can become stuck. Open the thermostat and then tap the side of each thermostat for a few minutes. Use something like a plastic hammer to tap them with. Very often this will release a stuck valve and you should have heat again. Radiators were not meant to be left on the same setting all the time. This could be the source of the problem.
3. You are probably not responsible for the replacement of the thermostats. Look at your lease to see what it says. Most leases say that the tenant is responsible for normal maintenance of plumbing. This generally refers to fixing leaking faucets, changing filters etc. In my opinion the landlord would be responsible for replacing a thermostat which is not working.

If they had to be left on 2 all the time there would be no 1 and no 3 or 4. I agree with Bruce that it could be air, stuck or clogged. Five thermos don't go off just like that at the same time.

AS suggested already it sounds like you need to bleed the radiators. You will find the little key required somewhere around the house and if not at Brico.
Five thermostats going off at once ...BS! You need to change the plummer not the thermostats!