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Thermostats aren't reading correctly

cah1151 Member Posts: 5
I have forced hot water in my home with baseboards.  It is a 3-zone setup.  One zone was installed two years ago.  At the time all zones had their thermostats replaced with new ones.  This year for the first time all three thermostats seem to be off varying degrees when I try to set them.  One is five degrees off, one is four degrees off, and one is two degrees off.  I am baffled by this.  Last year on any zone when I set the top part to 70 degrees the bottom setting showed 70 degrees.  This year in order to get the house temperature to be 70 degrees I need to set each one higher than I actually want it to be.  The heat does feel like 70 - it isn't too hot like 74 or 75 - and it does shut off properly.  Everything seems to be working well and heating well but this thermostat thing bugs me.  Is there anything I can possibly adjust or should I just accept this the way it now is?    


  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    What make are the thermostats

    and model numbers? Are they all the same? Are they mercury thermostats? If so they may need to be leveled. A picture would help also if you can.
  • rlaggren
    rlaggren Member Posts: 160
    What changed since last year?

    Always the first question.

    Not a heating pro, but had to solve lots of problems.

    Those Tstats all run down to the same controller, right? They _all_ act different, but they're not, like, all in the same room or anything... So. Might look at what's changed downstairs.

    Or... did a painter get onto all the walls where the 'stats are mounted?

    Anyway, sounds like something changed for all those stats.

    Cheers, Rufus
    disclaimer - I'm a plumber, not a heating pro.
  • cah1151
    cah1151 Member Posts: 5
    The make and what changed

    Thank you for your replies.  Tim, all three thermostats are the same.  They are Honeywells, Model T87K1007 and I will attach a picture I found online.  I'm not sure if they are mercury or not.  They seem to be level to me but I'm not positive.  Rufus, I am attaching a photo I took of our setup.  I'm not sure if they all run down to the same controller.  Maybe you can tell by the picture.  No, a painter didn't get onto the walls but I do now remember something.  And it is a change so maybe that's the problem.  We did have a pipe replaced.  In the picture it is the front pipe on the left that is gold.  Could the plumber have done something wrong?  I think I recall that he bled the system, etc.  Like I said, our heat is fine.  And the zones shut on and off like they should.  Is there an adjustment somewhere that I need to make to get my thermostats back to normal again?  Or do I need to call the plumber back to do it?  Thanks for your help.  Carol      
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,281
    I will start with this

    I like Honeywell products and they stand behind their products. That said I have had less than a perfect track record with those thermostats in the past couple of years. It may simply be the thermostats. Contact Honeywell.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • cah1151
    cah1151 Member Posts: 5
    Still puzzled with my thermostats

    But Charlie do you think there could possibly be something wrong with all three thermostats?  I could see one.  Or two maybe.  I've had Honeywell thermostats in my home for over 30 years and I have never had a problem with any of them.  The fact that I had a pipe replaced must have something to do with this.  What do you think?  Could something somehow be out of whack with my boiler setup now?  Today when I came downstairs it read 67 on one thermostat and I had to push it up to 72 in order for it to turn on.  On my other one it read 68 and I had to push it up to 75.  I'm a bit scared now.  Gas always makes me very nervous.  I can't reach the plumber - he was a friend of my son's.  He was licensed and all but he is now out in California.  Shall I try to call another plumber or a gas company person? 
  • icesailor
    icesailor Member Posts: 7,265
    T87 Thermostats:

    These are non mercury, electronic thermostats.

    I don't have one in my hot big hand at the moment but they work by "Cycling" so many times per hour. I think they have a adjustment to set them to cycle properly for the type of eqiopment you are using. Do you have Taco zone valves? They are power stealing valves and may be affecting the operation.

    I don't think that these thermostats will ever be as accurate as the old T87 mercury ones. They were really precision instruments.

    Another example of the laws of unintended consequences. No good deed goes unpunished.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    edited November 2010
    cah 1151 I would get in touch with

    Honeywell, you can get them on the Internet at www.customer.honeywell.com they also list an 800 number there.

    My experience with those thermostats is that the temp you read on the thermostat versus what is being controlled inside the t'stat are two different things. It is important that correct wiring and interface with controls is carried out and preliminary settings on the t'Stat were done correctly.

    Pull the cover off the front of T'stat in the upper Left hand corner are some switches labeled 1 and 2 Switch 1 should be in the off position and switch 2 in the on position for your system. That will give you approximately 3 cycles per hour  at 50% of heating load which is about 20 to 30 degrees outdoor temperature. See if that helps.
  • cah1151
    cah1151 Member Posts: 5
    Thanks for your help

    Tim, I checked the switch positions of the three thermostats and they are all set correctly.  I'm going to give Honeywell a call.  Thank you for all your suggestions.  And icesailor, yes, I do have Taco zone valves.  I had no idea that they are power stealing.  For my own peace of mind I just may have to have someone come over and check these things out for me.  I appreciate everyone's help!  Carol 
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    Carol seeing that you

    have Taco Zone Valves there is resistor that may need to be added to those to help resolve your problem. I do not have the number handy but can get it for you by tomorrow.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    Got the numbers

    from Honeywell web site. The resitor part number is 4074FAB and it should be wired across terminals 1 and 2 on the Taco Zone Valve.
  • cah1151
    cah1151 Member Posts: 5
    Resistor info

    Thanks for the part number and for the information on the resistor.  I truly appreciate it! 
This discussion has been closed.