Home thermostat doesn't respond to changes in temperature......

[hrricane34]

We have a modern digital thermostat that we mainly use during the summer months and we have noticed that if we have all the windows shut then the temperature (on the thermostat) does not change as the temperature of the room changes (we measured room temp independently of the thermostat). But the kicker is that if we open a window, even only a couple of inches (just has to be one of them, not all) in the house, the temperature on the thermostat would change quite rapidly and then settle to the actual room temp. Also note that the outside air is not any cooler than the current inside temp.

Based on an internet search all we could come up with is to insulate the area inside the wall where the thermostat is located since they seem to think that there is warm air blowing within the walls, but I'm not sure why opening a window would cause warm air to escape in between the walls behind the thermostat.

Does anyone have any other ideas as to why the temp only changes when we open a window?

[Ken]

Where is the thermostat located?? Is it on an interior wall? Is it near a stairwell? It's location can make a big difference as well as the effect of the mounting area. I had a situation where my thermostat was above a stairwell, and moving it some 8 feet made a world of difference in the regulated temperature upstairs.

[Tony Hwang]

Hmmm, Remove the 'stat off the wall and let it dangle away from the wall. It'll prove on your idea. Mine is wireless, I can place it any where in the house. Usually I locate it upstairs in summer and down stairs in winter.

[despen]

Check near the thermostat with incense or a piece of lit rope. Anything that makes smoke. Might as well just take it down and seal the holes the wires come out of.

Opening a window will change room pressure to outside pressure possibly changing air flows in the house.

[hrhofmann]

With the room set up so that the thermostat doesn't seem to be registering the actual room temperature, wave a large piece of cardboard in the vicinity of the thermostat so that the moving air goes around the thermostat. Maybe the air in the room is stratified and unless there is a door or window open, the air simply does not move enough to get into the inside of the thermostat where the sensor is located and cause it to be correct.

[trader4]

Is it reading higher than actual or lower and by how much? Hard to imagine it would not change at all in response to changing room temp with the windows closed. Are you saying it can actually be 80 in the room and it reads 72, then suddenly changes to the correct 80 when you crack a window open? Has it always been this way or is this something new?

As others have pointed out, if there is a hole in the wall behind the thermostat that allows a draft from the wall to occur, that can affect the thermostat. But this would be an extreme case of that occuring.

[bfrabel]

Some thermostats do what I think you are describing on purpose. They sense a small temperature change, turn on your heating or cooling, and the display will say always say the same temperature, as long as it doesn't drift more than a few degrees. It is a little tick to make you think the thermostat is working better than it really is. I know that Honeywell Vision Pro stats do this. Others probably do this too.

[trader4]

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I have several VisonPros here and they do no such thing. If the room temp drops a degree or two they show it. Also, how would you explain that the thermostat does in fact change as soon as he cracks a window and then settles at room temperature?

[bfrabel]

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Some thermostats (Vision Pro and others) do indeed round the displayed temperature to the setpoint temperature if it is only a couple of degrees off. Most people would never notice this and Honeywell doesn't print this in the owner's booklet, but they will tell you if you call them and ask them about it. My guess would be that they are programmed to not show the temperature change if it happens slowly and it thinks it can recover in a reasonable amount of times, but if it happens quickly it will show the actual temperature.

[trader4]

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Nonsense. Have 3 of them here and they respond fully to the actual room temperature as measured by other devices. Temp gioes up by 1 deg, my VisionPros show it. They are one of the most popular high-end thermostats and if they didn't show the actual room temp to within a degree or so, I'm sure we'd be hearing about it.

I would

I've found their customer service to be abysmal. For one thing, if you're not a dealer they won't even answer an install question. They told me I have to have an installer come over if I want to change a parameter. Makes me not want to buy another Honeywell product

Assuming they do behave as you describe, then why when the OP cracks a window do they suddenly behave differently?

[micky]

Does it go up or down?. I don't have a handle on what is happening.

But it sounds like the display numbers are stuck and need a push from t he outside air. Best to oil the numbers every year.

[Josh]

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We have 2 of these -- if the heating/cooling is off, or the actual temperature is more than a couple degrees from the setpoint, it does show the actual temperature accurately. But if on, it will "cheat" by a degree -- if cooling to 73, it will let the actual temp go to 74, still showing 73. If you bump the setpoint down or up, all of a sudden it shows 74.

This has been documented as a design feature on HVAC forums, and I think the installers manual even mentions it; I'll have to look at the docs I got with our system. It allows the system to cycle properly, while making people fawn over how great this thermostat is at keeping the temperature right at the setpoint at all times :-)

I do notice that "73" doesn't always feel like 73. In the end, it's not doing anything different than any other thermostat (all of them allow a 1-2 degree hysteresis), just showing a different value.

I'm not sure this has anything to do with the OP's observation if the unit is "off" (which is how I read it when he says the temperature itself is changing); when off our Honeywell tracks the temperature accurately.

Josh

[Evan]

Drafty wall cavities, large hole behind the thermostat which is effecting the thermostat's readings...

It would be nice if all the wall cavities were sealed up in your house but that is not required in single family homes...

I would seriously worry in the event of a fire in your house, if it gets into the walls at all it will end up causing a lot more damage as if this sort if airflow can have a significant enough volume to effect your thermostat reading, it will literally suck the fire into the walls if you leave the door open in your hasty retreat for your life or after flash over in a room breaks out the window...

~~ Evan

[trader4]

Another example of a vivid imagination run amuck. I suppose because the thermostat isn't reading correctly, for some unknown reason, the whole house should be condemned.

[clare]

Easy way to find out if there is anything to the "warm air in the wall" arguemnrt. Unscrew the 'stat from the wall and see what happens.

[trader4]

ide quoted text -

Yeah, that's one thing that could be tried. So much of this makes no sense. Not much pertinent info given, ie how far off is the thermostat from other thermostats? 1 deg? 5 deg? It also seems odd that if that's the problem that opening one window a bit suddenly makes it read the correct room temp. You would think if there were an air hole in the wall or something like that then opening a window would probably make it worse.

And what happened to the OP?