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Honeywell T87F Thermostat

Was having problems with heater shutting off without reason. Hoping the termostat was the fix, I took the outer cover off and saw a little calibration scale, I moved it back and forth and put it back where I thought it had started and then I heard the heater kick back on. I beleive it is fixed, but I was hoping to know what it is I did, or more so what that calibration scale is and how to use it correctly.

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This calibration is called the heat anticipator, this is set by the amp draw pulled through the t-stat,if you look very close at the scale you will see the word longer with an arrow ,if you push the lever in the direction of the arrow the heat will run longer .This is a very old style t-stat and is most likely out of calibration on the temp reading for the room, think of this portion of the t-stat as a stand alone thermometer,it may read 70 when the room is 74

Posted on Jul 02, 2013

5 Suggested Answers

  • 1420 Answers

SOURCE: boiler will not shut off

Boilers are controlled by a few things, one being a thermostat, secondly a zone valve or circulator control and thirdly by an Aquastat that controls the boiler temperature and safety shutoff. If one of those controls is sticking, your boiler will turn or remain on until it reached a temperature where the safety control shuts it off. If your boiler is not shutting off at all, most likely it is the Aquastat control. The Aquastat will be located on the boiler and may have "Honeywell" printed or stamped on it. Take off the front cover and you will find model numbers on the backside of the cover. If you have some mechanical skills, you could probably replace it. Turn off your power first and wire it wire per wire.
If your boiler is shutting off on high limit, I would suspect a stuck zone valve or circulator control or a bad thermostat or shorted thermostat wire.

Posted on Nov 15, 2007

  • 1420 Answers

SOURCE: Thermostat not working

Chances are that the fuse in the furnace blew. Remove the inspection cover on the furnace and look for a 3 amp fuse either in-line of the wiring or on the control board. Also check the circuit breaker box.

Posted on Nov 21, 2008

  • 27 Answers

SOURCE: Honeywell PRO TH4110d Prog Thermostat not responding

cfheck to make sur ethat the t-stat is set for your type of heat. if you do not go through the instructions sep by sep then you will have problems. if you have then call a professional.

Posted on Nov 26, 2008

  • 6966 Answers

SOURCE: Dy/night heater turns on for 10 sec then and off, over and over

Hi and welcome to FixYa,

If I understand your concern, it is that the heater switches itself on for 10 seconds and then switches itself automatically off. A couple of ideas of you may want to explore/check:

  1. the built-in protection system detects an internal fault and to prevent any further damage switches itself off;
  2. the faults could be:
  • open heating element (assuming it is electrical);
  • blower not turning;
  • open limit switch. The limit switch is an inline cutoff to the heater that automatically opens up when the heater exceeds a pre-determined temperature independent of the settings in the thermostat. This is like a thermal fuse once gone bad will remain open;
  • whereas a thermostatic switch will turn on if temperature is below its threshold and turn off if the temperature is above. It is basically an on/off switch.
Often the limit switch would look like the image below.
To be able to provide a more detailed information/assistance, pls verify & post back the model number of the Day Night Heater. Model 8ou-19 does not turn up anything. Or perhaps you can share the website you were referring to.

Good luck and Thank you for using FixYa. Happy Holidays.

Posted on Dec 21, 2008

  • 108 Answers

SOURCE: Replaced mercury thermostat w/Honeywell CT87K - doesn't work!

You need a specific thermostat for a Wall Furnace it is a Millivolt Thermostat and not a 24v standard thermostat....usually it will work anyway however if the powerpile (generator produces millivolts from the pilot light) is weak it may not be producing enough...or the Pilot light may be dirty and lazy...won't produce enough millivolts ...or you can have bad or dirty contacts or connections....or a combination of any of the above.....a 24v Thermostat and particularly a non-mercury thermostat has too much resistance in it for a millivolt your Wall Furnace (other than the fan) runs on less than 1 volt

Posted on Oct 31, 2009

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Without Batteries, they would not work.

Bingo!! It might be one of the reasons.Change the battery and see if that would fix the issue.

If problem persists, let me know.

Hope i helped you.

Thanks for using ' Fixya ' and have a nice day!!

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