This is a Tempstar ntv6050fb. It is about 12 years old.
On a cold day or when the house has been allowed to cool down, and
then the thermostat is turned up, the furnace starts up and runs
properly for several minutes, then the gas shuts off, and the eductor
fan goes to high, and the furnace relights. There is virtually no
The fact that it relights right away - and then runs fine for some
time (not sure if it does it a second time after 5 or more minutes -
usually gets up to temperature fairly quickly and then shuts down
normally) leads me to believe it is not likely cycling on limit, or
I have not cleaned thesensor.
Filter is kept clean and the problem has happened even when the filter
had just been washed (washable electrostatic)
Would this be "normal" behaviour if the furnace had run 12 minutes on
low fire and then went to high fire??
Does the gas shut off (momentarily) when the gas valve switches from
low to high??