ritetemp programmable stat
 

I installed a ritetemp prog stat to replace one of the old round ones. it was working just fine with the program that i set it up to do. but now the furnace comes on for a few minutes and then goes off, never reaching the set temp. if i overide the temp to a higher heat, again, the furnace comes on for a few, then goes off. example, i have the stat set to 16deg C for during the day when no one is usually home. i get home early, before the stat is programmed to go up to 20deg C and manually override it to go to 20. the furnace kicks on for a few minutes, then goes off. the furnace is about 16 years old. any suggestions? thanks in advance.:thumbsup:

Will it maintain the required Temp when left alone,..??

When the heat turns on, is there an icon (arrow, flame, etc.) that appears? Check to see if the icon is still there when the furnace turns off. If it's still there you likely have a furnace problem.

Thanks for that quick response.
1.
"When the heat turns on, is there an icon (arrow, flame, etc.) that appears? Check to see if the icon is still there when the furnace turns off. If it's still there you likely have a furnace problem."
Everything was working for about a month prior. On the stat, it only shows things like what the current temp is and temp that you want it to be. there are not any icons, just numbers, regardless whether it is on or off.
2.
"Will it maintain the required Temp when left alone,..??" No. if i have it programmed to go to 20deg at 5pm, the furnace starts up only for a few minutes then turns off again. this is when the house is currently at say 16deg. it never gets to the 20 deg, even if i turn off the auto and turn on the fan.
3.
"Sounds like you have a furnace problem, not a t-stat problem."
I was afraid of that, but was hoping it was the t-stat. i guess i could try putting the old one back on and see if it changes things. if this does not work, do you guys think it will be a complete replacement of the furnace, major work, or something minor.
4. again, thanks for the quick responses, i appreciate it.

Mike, it's really hard to say what the issue could be. Trying out the old thermostat is a good idea. What is the make of your furnace? Is it a high efficiency? When I hear "furnace runs for 2-3 minutes" I check to see if the furnace is overheating. Make sure no return air grills are blocked and your filter is clean. Also, open all of your vents. Let us know if that extends the run time.

Take the red and white wires at the stat and jump them out and see if the furnace stays on. If it cycles off with the wires jumped out then you have a furnace issue. Look for dust corrosion on the flame sensing rod.

When was the last time you saw a 90% with a T87?
Guess again.