Normal operation: Thermostat @ 70F, furnace runs until it hits 70-71F, then you can hear the gas valve/flame shut off while the fan continues to run for another minute or two, then turns off.
Problem: Thermostat @ 70F, furnace runs until it hits 70-71F, then you can hear the gas valve/flame shut off while the fan continues to run. HOWEVER, about 10 seconds after the flame is off and while the fan is still running its shutdown cycle, the flame reignites, runs for another minute or so, and keeps repeating this process. This repeats 3-4 times per heating cycle before it cuts the flame and allows the fan to run and turn off normally.
This happens with a Nest smart thermostat and a non-programmable battery operated thermostat. Also tried hardwiring heat power wire (Rh) to heating call (W). Furnace runs normally from 68F to 75F with no interruptions or odd behavior.
So thermostat and any thermal protection on furnace is ruled out. It's acting almost as if the temperature it's reading falls down to it's turn on temp of 68F immediately after hitting its target temp of 70-71F and switching into the fan cooldown step. Ideas?
Problem: Thermostat @ 70F, furnace runs until it hits 70-71F, then you can hear the gas valve/flame shut off while the fan continues to run. HOWEVER, about 10 seconds after the flame is off and while the fan is still running its shutdown cycle, the flame reignites, runs for another minute or so, and keeps repeating this process. This repeats 3-4 times per heating cycle before it cuts the flame and allows the fan to run and turn off normally.
This happens with a Nest smart thermostat and a non-programmable battery operated thermostat. Also tried hardwiring heat power wire (Rh) to heating call (W). Furnace runs normally from 68F to 75F with no interruptions or odd behavior.
So thermostat and any thermal protection on furnace is ruled out. It's acting almost as if the temperature it's reading falls down to it's turn on temp of 68F immediately after hitting its target temp of 70-71F and switching into the fan cooldown step. Ideas?