Replaced thermostat in smaller bedroom and tested operation. Tested operation. There are three zones in this house. One actuator is in the boiler room. The other two are under the master bedroom and the other bedroom that has the thermostat in it in the crawlspace . Ultimate Heating Tune-Up Gas Heat: serviced and inspected gas heating system checking Water flow checked pump oil pump clean burners checked combustion verified. All safeties are working. Couldn’t see any issues as far as water damage on the heat exchanger. Drain pressure tank as boiler pressure was almost 30 psi which is when the pressure relief valve opens. Pressure relief valve was connected to sewer drain. This is not supposed to be connected to anything so I made adjustment and cut it short so it’s per code. Carbon monoxide 81 ppm 8% oxygen stack temperature 460°