There are two main reasons that a heating system may not be compatible with nest thermostat.
Nest not compatible with high voltage.
It learns your habits and is controllable using smartphone applications when situations arise and you need to change the settings.
It s high current or a proprietary system.
In some cases it is possible to make a high voltage system nest compatible.
The 2018 nest learning thermostat 3rd generation is not only compatible with high voltage systems but it works as your best friend who is an agoraphobe and never leaves the house.
Contact a local pro and have them install a step down transformer to 20 30v.
High voltage thermostats are usually labeled 110 115 120 or 240 vac note.
While most heating systems are high voltage usually 230v usually they only use a little bit of current at a time up to 3a.