Radiator's not working

Hi, I am experiencing continual problems with my boilermate system, which was installed in my new build house 3 years ago. At the moment the radiators downstairs are not working, but previously it has been the upstairs ones.(2 temp controllers in house for different floors) Luckily I have an insurance policy, they have been out frequently to fix it. I have had valves(?) or the motor which moves them replaced numerous times, and this may last a couple of weeks, also we have had a new motor put on, this lasted 2 days.

Is there something that these engineers are missing?

Many thanks for any help in advance.