Ultimate Heating Tune-Up Gas Heat: serviced and inspected gas heating system checking air flow, temperature rise, electrical, gas pressure, safeties, controls and limits, heat exchanger and venting. cleaned and checked system components to manufacturer specifications and performed combustion inspection. Mounted wired and programmed supplied thermostat. Started and tested system on new thermostat. Repaired vent pipe at furnace as it wasn’t installed properly and was leaking. Gurgling sound is because whoever installed this equipment put a 3 to 2 reducer on the vent pipe in the horizontal position instead of vertical. I don’t think it’s going to cause much of an.