Tuya Smart Home automation: control of central heating boiler based on temperature difference

I need to create an automatic control system for the central heating boiler based on the difference between the temperature in the central heating tank and in the solid-fuel boiler. Namely, when the temperature in the central heating tank is higher than the temperature in the boiler it will switch off the relay and when it is lower it will switch on the relay which controls the valve.
Unfortunately, I am just starting out in Tuya / Smart Home.

You need a solar differential thermostat.

I already have a thermostat connected to a socket which measures the central heating boiler temperature and possibly activates the electric heater as well as a boiler temp sensor with switching on the central heating valve relay from the boiler and I have an automatic control system which switches on the central heating valve when the boiler temp rises above 60 i have an automatic system on it that when the boiler temp rises above 60, it switches on the valve for heating the central heating boiler but I would like it to do it on the basis of the temp difference and not on a fixed basis, e.g. boiler 70, boiler 74 off and similarly, because on sunny days I heat boiler 74 with a heater and I would not like the boiler to suck out the temp when the boiler is 60 and the boiler 70