T-stat stops call for heat before set temp reached

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  #1  
Old 12-04-18, 06:56 PM
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T-stat stops call for heat before set temp reached

Well, the title says it all. I have a relatively new "Orbit" programmable thermostat that's been working well. Tonight I noticed that when I raise the set temperature above the programmed temperature temporarily, the t-stat will kick on a call for heat for roughly one burner cycle then stop the call for heat before the temporary set temperature is reached. I tried turning off the t-stat, re-setting, etc, but the issue persists.

We did have an oil line replaced today, but all seems well with the burner, pump, etc. (it's firing and not in need of a reset). The tech did play with the Taco zone valve to turn on the boiler (same zone we're experiencing issues with), but the system worked fine for 5-6 hours after he left, so I'm not sure if that's the issue.

Can a zone valve or the boiler "talk to" the t-stat and stop a call for heat for any reason? If not, then I think the issue would have to be with the t-stat, correct?
 
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  #2  
Old 12-05-18, 05:13 AM
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If this is the first time using this feature. maybe its working as designed. Reread the owners manual. If not clear, call the manufacturer. Does the t'stat maintain the programmed temp? Difficult to fix something that isn't broken.
 
  #3  
Old 12-05-18, 05:37 AM
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I've used this t-stat for 2+ months so far - the programming isn't complicated and it's worked as intended up until now. There's a program set temperature and you can temporarily override that temperature by increasing or decreasing the t-stat temp. This will call for heat (in the case of an temp increase) and hold the "temporary" temperature until the next set temperature in the program.

My issue is that when I increase the temperature a couple of degrees (68 to 70), the t-stat calls for heat, the burner fires, etc., but the t-stat stops the call for heat in 5-7 minutes, still at 68 deg. It does seem to be holding the program set temp as of this am.

Can a zone valve or the boiler "talk to" the t-stat and stop a call for heat for any reason, or is that only dictated by the t-stat? Just trying to narrow down possible variables to troubleshoot.
 
  #4  
Old 12-05-18, 09:27 AM
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The thermostat sends out 24v to the valve. There is no return communication.

Typically there is heat icon that comes up on the screen when actually calling for heat.
If it has that...... is it staying on and there is no heat or is that turning off ?
 
  #5  
Old 12-05-18, 09:56 AM
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I would test with a bigger spread. I would set the program to drop the room temp to 65, and then try the temporary override feature with the setpoint at 69 and see what happens.
 
  #6  
Old 12-05-18, 10:36 AM
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"The thermostat sends out 24v to the valve. There is no return communication."

So, I presume this points to the thermostat having some sort of issue...

"Typically there is heat icon that comes up on the screen when actually calling for heat.
If it has that...... is it staying on and there is no heat or is that turning off ?"


It is turning off (ending the call for heat before reaching the set temperature)

"I would test with a bigger spread. I would set the program to drop the room temp to 65, and then try the temporary override feature with the setpoint at 69 and see what happens."

Ok - what will this tell me though? It was working fine with a 2 degree override (actually worked with just a 1 degree override) until yesterday. Seems to me the t-stat should not stop a call for heat until the set temp is reached no matter the difference, but I can give it a try if it's helpful from a troubleshooting sense.
 
  #7  
Old 12-05-18, 12:20 PM
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What brand of zone valve do you have. Taco is not compatible with all stats because of the high amperage they draw which is .9amps. That is almost double of others. They do make one now that takes less amps to open just for informational purposes.

If the amps are too low it will not open or will open and close which will kill the power to the burner or make it short cycle but your stat should still be calling through all of this.

What you can try is remove the stat and jump the 2 wires together initiating a call for heat and if the burner stays running you know it's in the stat.

Some stats come with a separate resister that must be installed if a Taco Zone Valve is used.

Hope this helps a little.
 
  #8  
Old 12-05-18, 06:20 PM
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it (heat emblem)is turning off (ending the call for heat before reaching the set temperature)
Then that is strictly a problem with the thermostat.
I've never used those Orbit stats so can't help you much on their issues.
 
  #9  
Old 12-05-18, 06:42 PM
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Just a guess here, but maybe it has something to do with the T-stat's "heat anticipator"...?

What's a Heat Anticipator?

A heat anticipator, found in some room thermostats, is a tiny heater that warms the thermostat to cause it to turn the heating system off a bit before the room has actually reached the set-temperature on the wall thermostat...

A heat anticipator is used to avoid room temperature overshoot.

Source.
 
  #10  
Old 12-05-18, 07:32 PM
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R,
That's what I described in post #7 but I was trying to avoid a foreign word that I would have to explain but that .9 amps is the heat anticipator setting needed for Taco ZV's which is the highest amp. draw for a ZV that I know of.

The new digital stats generally do not have adjustable heat anticipators anymore. They say they should be compatible with any control up to 1 amp but it's been found not to be true.

I've called Honeywell in the past over some issues and although they will not put it in writing some of their stats would not work with Taco ZV. These issues were quite a while back. I'm not involved like I once was, maybe it has been straightened out but just thought I'd mention it.

Found this review if this is what you have.

The Orbit programmable timer is a compact and good looking timer. The unit is easy to install and program. Once you get the instructions out, you may find out that it doesn't work on your heating system. This timer doesn't work with Heat pumps that have auxiliary/backup heat, such as gas or electric. It doesn't work with 3 wire hydronic, multi stage heating or cooling or baseboard heat. That fact eliminates a lot of systems, which isn't mentioned until you get it out of the package. If the packaging mentioned that it doesn't work on many systems, it would be a better unit. I'm sure many of these will be returned once people realize it is not universal as other units.
 

Last edited by spott; 12-05-18 at 07:52 PM.
  #11  
Old 12-06-18, 07:52 AM
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Anticipator is what I was thinking. If it's one of the programming options maybe it's set for a fast response system like forced air, while you have a slow response hydronic system.
 
  #12  
Old 12-07-18, 05:41 AM
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Hi, if it were the heat anticipator I would think it would effect the operation all of the time, ie programed settings.
Geo
 
  #13  
Old 12-07-18, 06:04 AM
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Settings are all correct - as for the t-stat not working with baseboard heat, that doesnít seem to be true as we have oil fired hot water baseboard heat and before this issue the Orbit t-stats were working fine (2+ months).

in any event, the t-stat seems to be functioning properly as of last evening. Oddly, in an exhaustive internet search, I didnít find any instance of someome
complaining of a similar issue (t-stat ending call for heat early). Weird.

If it happens again Iíll turn it off and reset it - if there is anything I learned from troubleshooting electronics itís that resetting / restarting solves 90% of the issues.

 
  #14  
Old 12-07-18, 06:06 AM
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Have you replaced the batteries?
Geo
 
  #15  
Old 12-08-18, 08:02 AM
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Might just be a firmware bug (or the old joke in the day when I did SW, it’s not a bug “it’s an undocumented feature”). Could be that when you moved the setpoint up to 70 while the current temp was 68, the right hand triggered the process to run the burner, but passed to the left hand (which runs the burner) the old setpoint (68) as the target, instead of the new setpoint .

Something like that can be triggered by very subtle conditions in the firmware, and then it can disappear. You would need the SW people to do some real heavy duty code analysis to find something like that. But if it doesn’t happen very often (and as you say you can’t find many instances of that reported) then probably no one will ever look for it.

Forgot to say, after thinking more about it, I think I had the same kind of problem when I put in my new Honeywell T'stat . Might have been a little different but I think the problem anyway was that the t'stat would not reach the setpoint. It just stopped or wouldn't call for heat for some reason. Haven't seen it for a while, but I just leave my t'stats at 62 and don't touch them. (I know yours isn't Honeywell)
 

Last edited by zoesdad; 12-08-18 at 10:13 AM. Reason: added "Forgot to ...
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