Weather compensation is set up, but just struggling with getting hysteresis set up. 

Im assuming from your original post that hysterisis refers to the DHW and you want it to reheat immediately the water temperature falls below some particular value as opposed to only on timer.

I wouldn't recommend this TBH, I would instead suggest having 2 timed periods, but if you are determined then this would be called something like 'constant' or 'dhw priority' or similar in the grant controller menu.  Probably in the installer menu only not the user menu.  Maybe a Grant expert will pop up who knows, otherwise it will be a trawl through the manual.

Like @grahamf I would consider dropping the TADO.  External controllers are usually not good for the efficiency of heat pumps, or indeed the level of comfort, unless they have been specifically designed to integrate with them and control flow temperature not just operate as an on/off signal.  To do this they have to be adapted to the particular heat pump model and I cant find any evidence that the TADO is, nor did the salesman claim that it was when I quizzed him at last year's installer show.  

Weather compensation is set up, but just struggling with getting hysteresis set up. 

You would probably be better off with the Aerona Smart Controller, rather than the Tado  Also, if you have not set up weather compensation, then I would definitely advise you to do so.  People on here can advise you how to do it.

I'm having some trouble with a Grant ASHP and Tado Smart Stat.

The heating has been temperamental for the last few days after we replaced the old heat pump. The hot water is currently on a timer and is working as expected, although we would like to have it set up on hysteresis, if you can do this on a Grant. It's a 17kW Grant R32, with a standard cylinder, and 3 port with just rads.

Thanks in advance for any help.