Good morning, there may be a few reasons for the fault.
Firstly the solar flat panels may have a build up of dirt which acts as an insulation and stops the suns rays heating up the water within the panels, using a ladder with some soapy water made up with algae remover, use a bristle brush to scrub the panels, this can often be all that is needed to remove the build up of dirt.
It may also be a case that your system has developed an air lock, resulting in the heat not being absorbed properly in the panel, there is often a bleed valve located at the highest point of the installation (typically the solar panel).
Lastly it could be a faulty thermostat, the reading your getting from the LCD may be incorrect and the solar panel is actually 70 degrees, other than using a temp probe on the solar panel there isnt a easy way to check.
Before calling anyone out, I would first give the panel a good clean and see if you see an improvement, if you would like me to recommend someone to come out please provide your postcode.
Should you need anything clarified please ask.