Ever since the cold spell has settled in here in central Pa, I have been having a problem.
Thermostat is good ole Honeywell, round, mechanical. I do not know what make or model furnace is. We bought the house last May and home inspector told us furnace looked to be around 15 yrs old. He did say the furnace looked to be in good condition. I have looked over furnace and can not find any information on it. There is one spot where there was a sticker, but sticker is gone. Furnace is gas, forced air.

The problem is the thermostat is set for 74 degrees and the furnace cuts off at 68 degrees.
The 68 degrees is the reading on lower half of thermostat. I also have a digital thermoter on my computer desk and it is reading 68 degrees. Thermostat has been accurate within a degree or two up to this last cold spell set in.

My question is: Does this sound like a furnace or thermostat problem? Should I just try replacing the thermostat first before I call for a service call?

Thanks

That good old round stat most likely has a mercury bubble inside to make its call for heat. Remove the round bezel and you should see the bubble. There are 2 or three mounting screws that hold the stat to the wall but also allow slight rotation. Loosen the screws and a slightly rotate the stat until the bubble makes a connection, you should see a momentary blue spark in the bubble. That spark should occur at a point when the room temp is about 1 or 2 degrees below current room temp.

Update:

We got up yesterday morning and temp in house was 60 deg. Thermostat was set at 75 deg. I set the thermostat for 85 deg. This brought the temp up to 64 deg. I ran to Home Depot and purchased another Honeywell CT87K round manual thermostat. I cleaned the end of wires at furnace end and thermostat end. Read 24 volts at thermostat. After I installed the new thermostat, I set it at 75 degs and waited to see what happened. The furnace kicked on and when it kicked off it was 64 degrees in house. The furnace is still cycling about 6 times an hour. We put an electric space heater in room for the evening. After awhile the room temp did come up to 75 degs. According to the thermometer on thermostat. Shut space heater off when we went to bed and was anxious to see what the room was when we go up. Room was 69 degrees this morning, this with thermostat still set at 75 degs.

Shouldn't furnace keep running until temp hit within 2 degs of thermostat setting? And what in furnace would cause it to shut down below what it should?

I for sure will not mess with the furnace, will call a tech, but was just wondering what could cause this problem...

Did forget to mention that outside temp these past morning has been 8 or 9 degrees F.

It is very easy to sort out furnace/thermostat problems. I am referring you to the sticky because it is a great resource once you determine what to work on.
https://www.askmehelpdesk.com/heatin...tml#post268260

The administration is encouraging experts to set up stickies in their forum. Among other advantages, it allows people to get the best AMHD has even when the expert is off line.

My forced air heating/air conditioning unit is 18 years old, this winter I have to set the thermostat at 77 degrees and the thermometer on the honeywell thermostat registers 77 degrees and cuts off as required but my house is still cold, especially in the furtherest room. What could be the problem,I had a new A-Coil installed last summer and the air conditioning works great and cools the entire hous as programmed.

Sounds like you could have two problems both based on insulation. Your home mayneed additional insulation. It is usually easiest and most effective to add batts to your attic. If you air ducts run through any unheated basement or crawl space you can add ridgid insulation to the ducts. In the meantime, try partially closing the supply registers closer to the furnace and the stat. This will force ,ore warm air to the far end of your run. Here is a side question. When you're a coil was installed did they do anything to the blower?