Furnace or thermostat problem?

If my thermostat's been set to 64 or 65 all day and I bump it up to, say, 68, I find maybe 20 minutes later that the house temp (measured at the thermostat) is still where it was before raising the setting. Sometimes a bit lower, because I also find that the furnace is blowing cold air. But before I raise the setting, the temp shown on the thermostat matches the lower temp it was set at before. So, I know that while I was away, the system was maintaining the lower temp correctly.
I've only noticed this for the past couple of days, and I've been too busy when arriving home to check & see if the furnace blew ANY warm air in the first few minutes after raising the temp. When it's functioning correctly, there's warm air within 30 seconds of the furnace turning on. With the partial information I've provided, does this sound more like a thermostat issue or a problem with the furnace?
The thermostat is an Aprilaire 8363 (digital, controls furnace and AC). Installed by reputable contractor. The gas furnace is a 12 year old Goodman installed by a contractor hired by previous homeowner. It's been serviced by my choice of contractor for the past 8 years.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Any batteries in the thermostat? Can you hear the furnace igniting when you raise the temp?
Does the blower start up about 30 sec after you raise the thermostat? If it does, that indicates that the furnace is heating up the air enough to start the blower.
You need to stop being so busy and think about the problem and let us know more!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Any batteries in the thermostat? Can you hear the furnace igniting when you raise the temp?
Does the blower start up about 30 sec after you raise the thermostat? If it does, that indicates that the furnace is heating up the air enough to start the blower.
You need to stop being so busy and think about the problem and let us know more!
========= Hey! I'm starving when I get home. Heat's the last thing on my mind. But it won't be if the thing dies completely this week. This is western NY.
On a positive note, I've been using the same contractor since 1982, and although I haven't needed them that often, the diagnosis is always really interesting, at least from the standpoint of someone who's nutty enough to find such things interesting. For instance, the slob who installed this furnace (came with the house) didn't properly angle the exhaust pipe (PVC, for high-efficiency furnace). I was hearing gurgling in the pipe. I'm sure any experienced homeowner would've had the same thought I did: The house is possessed and something's living in that friggin' pipe. Turns out there was water collecting in it, which caused a furnace symptom which I don't recall 8 years later. Whatever. It was interesting.
Stay tuned. I'll observe more carefully tomorrow when I get home from work. And, I'll check Le Battery. Or La Battery.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Dec 28, 9:05pm, "Stormin Mormon"

If you have it set to 64 and it's cold outside, after your bump it up, it could take 20+ mins for the thermostat to show 65. Worst case, the temp before it starts might have been almost enough to have the thermostat show 63. In which case it has to go up almost 2 degrees before it will show 65. I have a gas furnace that is on the large size for my house and it raises the temp about 5.25 degrees an hour.
The real answer to your question is to leave it off for awhile, then kick it up and go to the furnace and see what happens. The furnace should fire, and then a minute or so later the blower should come on.
Also, it';s not a two stage furnace is it? Don't know if they were around 12 years ago. But they are common today. And they can work two ways. First way is with a 2 stage thermostat, which IMO is the only correct way. Set up that way, the thermostat calls for either first stage heating, which is about 70% of full capacity, or full capacity. The thermostat knows how far the temp needs to go up and what the recent prior run history has been. So it can make a good decision on what to do.
The second way, is to just use a regular thermostat. In that case, the furnace always fires at the low rate first. You typically can set the number of minutes it will run on low to 5 or 12 minutes. After that, if the thermostat is still calling for heat, it shifts to full output. The obvious disadvantage is that is you have it set back to 60, come home and move it to 68, you're going to be waitingg 12 mins to get to full output. So, you'd see a longer time before the temp goes up.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.