My tempstar smartcomfort furnace turns on for only a few minutes when starting the heating cycle in the morning, It then shuts off. Then I hear a whine for about a minute followed the furnace igniting again.

This repeats itself for several cycles but then stops several degrees below set temperature.

Eventually it raises the house temperature but it can take a couple of hours.

A service man inspected and "unplugged C/A pipe, but there no change.

First off if you paid the service man and he did not fix your unit then he should come back and fix it correctly. You paid him to do a job.

It sounds like the flame sensor might be dirty or need to be replaced but it could also be many other things.

Thermostst heat anticipator setting for one will cause problems such as this.
Dirty furnace air filter will cause the furnace to cycle on high limit.
Closed registers or restricted cold air returns is another and the list goes on and on.

Thanks to those who answered. The solution proved to be a simple one. The hose carrying the water to the drain had a slight upward curve so it acted like a trap. The water backed up the hose and into pressure hoses the shut the furnace off. Once the hose was clamped down but not kinked, the furnace worked fine.

Thanks again.
Glenn10

Just glad you got it fixed

I figured the drain was OK since the service man just inspected it and unplugged the pipe as per your first post. That was a easy fix glad it is working.