Hi, i have a Brivis ducted heating unit (no...

Hi, i have a Brivis ducted heating unit (no idea what model)its a roof unit. when we first moved into the house, it worked for a period of time and then started to randomly blow cold air and no matter what we did on the control unit, it would only stop blowing cold air when it wanted to. so we turned off the power switch and left it for about 12 months. in a fit of desperation we turned it back on and it worked perfectly......for 48 hours and then went back to its old tricks. we reset the unit and it worked that night and the following morning and then it started blowing cold air (when it wanted to) and would not respond to ANYTHING that we did on the control. the pilot was lit but the fans wouldnt turn on nor would it blow heat. Any help would be greatly appreciated as Brivis want $200 just to walk through my front door. Thanks in advance =D