Solar power problems

[Solarafrica]

We are off grid. We have 4 pv panels providing between 30v and 38v (depending on time of day, according to the electrician). These power 2 12v 200ah batteries and we use a 500w inverter (Studer AJ 600). Our charge controller (Vitron Blue 100/30)has stopped working and no longer regulates the charge to the batteries. We have dismantled the system to stop overcharging. The installer of the charge controller says the problem is that the panels are not producing enough power but this doesn't seem right as the batteries are always fully charged (normally registering between 25.8 and 28.4 on the voltmeter before the charge controller goes to float). We are being bafgled by incomprehensible technical data. All we want is either for the installer to replace the charge controller or we buy a different one. Please advise. Is our solar power system wonecthat should work? It has been working fine for more than a year...