I currently have a solar thermal system which uses two controllers: Resol DeltaSol BS Plus and Barilla Solar STDC.  

My system has developed an issue whereby there is a long lag in the controllers' sensors detecting a rise in temperature in the system when the pumps are not running.  An imperfect solution to this is to replace the controllers for controllers which have a time-based start up function rather than a temperature change based function (which is what these two controllers have).  

I have been looking at Resol DeltaSol CS/4 to replace the Barilla STDC because that system only has one store and the Resol DeltaSol CS Plus controller to replace the BS Plus because that system has two stores.  

Does anyone have any advice on the 'best' controllers with a timed start up function?  Are there particular advantages to stretching to the Resol DeltaSol SSL Solar Controller?  

Any advice very welcome.  I am new to this area of technology.