Temp set to 64. 5 day programmable Honeywell from Home Depot. Had worked fine for over a year.
Woke up at 50.
Heat kicks on, got to 54 then shut off.
I adjusted temp to 74.
Still went to 54 then shuts off.
Heater never blows for more than a few minutes.

Decided to go to simple thermostat (round manual Honeywell).
Manually set to 74.
Heat went on and got as high as 58-60 but won't stay on any longer.

Family got home from work - house 54.
Called in gas company.
They Changed igniter last night. Commented it was dirty.

Read previous postings on this site and saw about changing air filter.
It was pretty dirty so I did it.

Turned heat on - and the heat came on but is still shutting off well before reaching temps.
Now weekend - hate to call in pro's but its too cold.
Are there any other basic things I can try (only a modest DIYer)
BTW - settings on the thermostat is for gas furnace.

Try running the furnace fan in the "ON" position at the thermostat, then turn the heat up and see what happens, this will tell you if you have a problem with the fan motor or low speed in the motor, post back what happens,Good luck, Mike

Thanks Mike for quick response.
Fan went on and blowing. Feels like the air is warm but not as warm as experienced in past. ALthough the duct work has gotten very cold so perhaps there is some lag in how warm it will get.
Also flow rate seems less. Perhaps my imagination.

After 5 to 10 minutes - I heard the fan kick off but there is some noise in the furnace like it is trying to do something - then the fan kicks on but only stays on for a minute or so.
Will report back later.

Your fan should be running continuously with the fan switch in the "ON" position , perhaps a bad motor?

I read in some other session about a possible blockage on some exhaust line? - is there an exhaust trap or other line that might collect condensate and freeze. We have been having temps in the 20's that have iced up or some critter nesting somewhere?