Unidare WMC718 not working?

We have two Unidare storage heaters in the apartment and both have stopped working. This happend a couple of weeks ago and I reset both units and turned them up full blast to make sure they were taking in heat. They worked for about 3 days (I turned the input down to 3 on both after the first day) and now they no longer work. I reset them again and turned up all the thermostat dials in the apartment but they still will not take in any heat. One of them is the WMC718 model which has a boost switch on the side. I turned the boost switch on about 3 weeks ago and it worked for about 5 mins before switching off. Now the light doesn't come on when I try to turn it on and no heat is generated from it. Any ideas what could be the problem with them? Is it something that I can fix or will it need a hefty call out charge from an electrician??