My wall mounted convector heater does not always turn on?

My new wall mounted Uberhaus convector heater does not always open when I turn on the thermostrat.I have changed the thermostat,checked all the wall connections to the heater and to see if if power is coming in from the thermostrat and everything is ok.

When the heater does go on it stays on for a while and goes off but never turns back on.If I try a couple of hours later to turn it back on,no reaction at all.

Could the wall heater element be the problem?