Came out to call for a system not heating properly. When I had contacted the landlord, he stated his tenant had said that it was starting to work again, but that he’d like me to check it out and that he would meet me there. Tenant had said that the thermostat was set to heat, but wasn’t coming on and the temperature was dropping. She said the set point temperature on the thermostat would go blank and not register. She also changed the filter yesterday. I checked the whole system over and found the thermostat set point temperature would go blank intermittently if you adjust the thermostat, and would come back on its own. Let landlord know that the issue is most likely the thermostat. Customer approved replacement of the thermostat to eliminate intermittent issues. I replaced the existing thermostat with a Honeywell T6. Adjusted settings based off the installed equipment and went over how to use new thermostat with tenant. Went ahead and cleaned the flame sensor and did a maintenance che