Is it possible to install DualSun SPRING panels to replace old thermal solar panels?

Yes, it is quite possible to install DualSun SPRING panels instead of thermal sensors.

However, there are two points to be aware of before installing hybrids : 

1. Check that the tank has a heat exchanger at the bottom of the tank with a thermowell in the middle of the bottom exchanger. 
2. During construction, before installing and connecting the panels, make sure that the entire solar circuit is thoroughly rinsed with clear water.

We recommend disconnecting the thermal sensors during this operation and connecting the input and output to each other to facilitate flushing.

Empty the pump tank when it is dirty and start again until clear water is obtained.

Finally, it is important to explain to the customer the difference in performance between a DualSun SPRING panel and a thermal panel:  How does the thermal efficiency of a DualSun panel compare to that of a conventional solar thermal module?