Direct UVC Question - Stats?!

[catrionag]

We have had a Telford Tempest 170L Cylinder installed, and have questions about the stat, or lack of. We've always had gas combi boilers in previous flats, so we're a bit clueless about how the cylinder is supposed to work - our sparky isn't a huge amount of help since he's unfamiliar with them.

 

We had been provided with this stat which came with everything else from Cylinders2Go https://www.tdlonline.co.uk/Heating/Hot-Water-Cylinders/Immersion-Heaters/58614-/Telford-Cylinder-Stat and were unsure what to do with it - when I spoke to Telford they said it had been supplied in error, and that direct cylinders don't need a stat.

 

The Cylinder has two immersions, both of them with a dial like the one in the picture attached. The lower one as I understand is the main immersion, and the top is a boost. Should the lower one be on all the time? How can you tell what temperature it's set to? And if it doesn't have an integral stat, how does it know when it's got to whatever temp you've set it to?

 

To complicate things, we have Solar PV being installed and are planning to set up a diverter so that excess energy generated by the PV heats up the cylinder. In this case surely we do need a stat to prevent it from overheating, but Telford only said that they didn't know and that we should speak to the solar installer.

 

Does anyone have a similar setup that could shed any light?