Where can I get driver for generetic z wave thermostat , is there code available somewhere ?
No. Code isn't available for any of the built-in apps/drivers. There are examples of some drivers and apps at Hubitat's github repository.
There are also many non-generic zwave thermost drivers out there to use as a reference.
Most zwave thermostats use the exact same capabilities, so are all 90% the same...
Pick any of them to use as a reference. I publish a gocontrol one on my github if interested.
There's already a generic z-wave thermostat drive in Hubitat. I've used it with my StelPro thermostat's. No source available though.
For source and a starting point look at the SmartThings generic driver. I'm sure it was the base for the Hubitat one.
i think that adding new value just to show in current status of valve is not very complicated for someone who is experienced coder