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Learning to use classic vintage Honeywell Chronotherm thermostat

CoachBoilermaker
CoachBoilermaker Member Posts: 347
edited December 3 in THE MAIN WALL

Outdoor temp is 53F.

Thermostat lower gauge indicates indoor temp of about 50F.

Red slider is around 65F

Why is the heat not kicking on? Heat is not on.

I know heat/boiler works b/c it will make steam if I exaggeratedly move the red slider to 80F.

Also, boiler fires up to keep tankless coil water heated.

But why isn't the boiler turning on as soon as room temp falls below 65F?

Broken thermostat or am I missing something obvious?

AC is not connected to this thermostat, just oil fed steam boiler.

I moved the blue slider to touch the red at 65F and still nothing.

«13

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,856

    Sounds to me like the thrmostat is either way out of adjustment — or busted. Or… not familiar with that model, but is their a changeover switch form cooling to heating which might not be set right?

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Grallert
  • hot_rod
    hot_rod Member Posts: 23,392

    That looks like an early Chrontherm stat? The blue was the temperature during setback, the red was the normal operating temperature. Slide them both past 65 or so. Does it kick on?

    Is there a clock dial on the left or inside with pins to set the schedule?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2
  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347
    edited October 17

    Boiler kicked on when I pushed it to 68. I had assumed it was 50F in the house, but the little display of room temp is just a spring. Not connected to system at all. For display purposes only. So, it might have been 67 for all I know. Next step is to compare room temp actual vs. temp slider. Could be calibration, as stated above.

  • HVACNUT
    HVACNUT Member Posts: 6,332

    Push the levers together. There's no setback so it's reading the Blue lever. Push them together at your desired setpoint.

  • hot_rod
    hot_rod Member Posts: 23,392

    The spring is a bimetal thermometer. Some of them have an adjustment to dial it in to actual room temperature.

    You are correct, it is not connected to the functionality of the stat. But it would be nice if it was accurate. Like a clock.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    Can you explain what "no setback" means?

    Blue lever gets priority?

    I was thinking blue=AC and red=heat.

    I might need to read the owner's manual.

    https://www.manualslib.com/manual/69908/Honeywell-T8090a-191108a.html?page=4#manual

  • HVACNUT
    HVACNUT Member Posts: 6,332

    There should be a clock with pins to place and make setback times to save fuel. The Blue indicator is the setback temperature, and the Red indicator is the "comfort" temperature. If you push the Red and Blue indicators together, it overrides the setback.

  • Robertw
    Robertw Member Posts: 27

    Make sure its level also. Its got mercury tubes inside of it that will be waaay off if out of level

    Robert W.

    Energy Kinetics

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    If you take the cover off completely (both the cover and the door you have lifted in that photo) you will have two mercury bulb switches.  Those switches are attached to a bimetal spring that changes its coil based on the temperature.  (Just like the thermometer you say does not do anything).  You can set the position of the mercury switches with the blue or red lever.  By setting the blue lever to 65° you will see that the mercury bulb will rock to the left as the temperature drops below 65° and rocks to the left when the temperature rises above 65°.  There is about a 1-1/2° to 2° differential on that swing from left to right and back again.

    Item 14 are the mercury bulbs on the bimetal coil.  The way a bimetal coil works is there are two dissimilar metals bonded together and spun into a coil. As the temperature changes one of the metals expands at a different rate than the other metal.  This causes the spring to change shape based on temperature changes.  The coil will get larger or smaller on a rotating motion.  That rotating motion will change the angle of the mercury switch. 

    There is also a heat anticipator adjustment that will provide a small amount of “FAKE” heat inside that thermostat to anticipate that the temperature may rise above 65° a little too far on some gravity heaters, and make the room 67 or more after the burner shuts off.  That is adjustable based on the type of heating system you connect the thermostat to. I is number 12 on the photo and has a more detailed illustration (Fig. 8) just below it. On that same note, The onboard clock also generates a little heat and the calibration of the thermostat takes that into account.   So if the clock motor is no longer operational, then your calibration will be off to the cold side by a few degrees. 

    If the small red and blue pinwheel at the lower right of the clock (number 8 on the photo) is set on blue, then the blue lever is what the thermostat is set on.   When the clock spins and you have one of the blue or red pins inserted at a given time, the small pinwheel will change to the Red lever to control the temperature.  As each hour passes the clock may change from the red lever setting to the blue lever setting based on where the pins are set on the 24 hour wheel.  Since you have no pins in the clock wheel, the thermostat will never change from blue to red or from red to blue.   By placing both the red and blue levers together. You are basically eliminating any set back because both levers will be set at the same temperature 

    I hope this helps in understanding your thermostat.

    As long as you don't need WiFi control of your system, and you can compensate for the accuracy of the calibration, you have a superior thermostat for a boiler like yours. Don't get rid of it!


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    PC7060Intplm.
  • HomerJSmith
    HomerJSmith Member Posts: 2,635

    Why don't you just buy a newer thermostat? Make your life easier. 14 on your pic has mercury in the bulbs and should be recycled.

    SuperTech
  • Jamie Hall
    Jamie Hall Member Posts: 24,856
    edited October 17

    I disagree. No newer thermostat will be as reliable or as last as long. So long as you don't break the mercury bulbs there is no hazard. None. Zip. Nada.

    Stop scaring people, @HomerJSmith , or if you must pick something real.

    Edit: cone to think of it, @CoachBoilermaker , if you're really terrified of it, I'll take it.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    delcrossvPRRIntplm.BrassFinger
  • hot_rod
    hot_rod Member Posts: 23,392

    As I recall some of them became noisey, you could hear the gear train mechanism at work.And the clicking when it flipped in and out of setback.

    looks like you are not using the setback, may as well get a nice large face, user friendly digital stat.

    Ecobee if you want a WiFi type thermostat.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTech
  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    Thanks for the info, guys.

    @EdTheHeaterMan @HVACNUT

    With this upcoming first winter, I will need to decide on what schedule I want to heat my house.

    It is just 2 of us in the house.

    When we are at work all day, I can have a low temperature mostly to prevent the pipes from freezing? (What's a good empty house all day temperature??)

    Then set it to turn on at 5pm. Then maybe low again at 10pm bedtime (space heater in BR? Instead of heating rest of empty house all night?)

  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347
    edited October 17

    Do you agree with GPT??

    ==========

    For your heating schedule, you're on the right track with lowering the temperature when the house is empty and possibly using a space heater at night. Here's a plan that could work well:

    Daytime (when you're at work):

    • Setback Temperature: A common recommendation is to keep the house around 55°F when you're away. This is warm enough to prevent pipes from freezing while still saving energy.
    • Pipe-Freezing Concerns: As long as your house is well-insulated and the temperature stays above 50°F, the risk of pipes freezing is low. You can also set up your thermostat to have a "minimum temperature" in case the weather gets especially cold.

    Evening (when you return home):

    • Comfortable Temperature: Set the thermostat to start warming up around 5 p.m. so that the house is at a comfortable 68-70°F when you get home.

    Nighttime (bedtime):

    • Setback Temperature: For sleeping, it's often more comfortable to lower the temperature again. You could drop it to 60-62°F around 10 p.m. and use a space heater in the bedroom if needed. This would save energy by not heating the rest of the house unnecessarily.
    • Space Heater in Bedroom: Using a space heater in just the bedroom is an efficient way to stay warm without cranking up the heat for the whole house overnight. Make sure it's a safe, energy-efficient model.

    Weekends/Days Off:

    • If you're home during the day, you could adjust the schedule to maintain a comfortable temperature, or just manually override the thermostat as needed.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    The common logic is that for every degree you can lower the temperature in your home your heat loss will decrease by 3%. So when you set your thermostat to 70° for comfort, changing it to 69° will yield you a 3% lower gas bill. That is what was advertised in the 1970s anyway. Now by setting your thermostat to 68° because President Nixon told you to, you would save out country from being dependent on OPEC and reduce your oil or gas bill by 6%. If you could turn your thermostat down 5° lower for half the day, (62° at night and 62° when away from home) you could save an additional 7.5% (5 degrees x 3% got 1/2 of the day = 7.5%). So the Chronotherm was reintroduced with a battery back up so the clock didn't loose time.

    then there were the folks that said this was all a government hoax and you lost all your savings when you turned up the thermostat to recover from the lower temperature. I have looked at this and did some unscientific tests on my own home back then and came up with this:

    If you lower the thermostat 5° for 3 hours then raised the temperature back up to the comfort temperature, you will probably not save that much. But any lowering of the thermostat more than 3 hours will result in a savings. To set back the thermostat 5° for 8 hours, there wil be 5 hours of actual savings. So when you go to work for 8 to 9 hours (including travel) you will save 2% When you set back 8 hours while sleeping you will save another 2%. That is a total of 4% if you remember to do it. and that is the reason for the setback thermostat.

    In the 2000s we called it a programable thermostat. Today we call it a smart thermostat

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • HomerJSmith
    HomerJSmith Member Posts: 2,635
    edited October 17

    @Jamie Hall , I'm not saying it is a hazard or that I am scaring people. I merely stated , if you discard the old mercury thermostat, to discard it environmentally.

    Bi-metal thermostats do get out of calibration and wear. If you have a thermostat calibration wrench and an accurate thermometer, good.

    The newer electronic thermostats are, I think, more accurate, responsive, reliable and easier to read.

    We stopped driving around in Ford Model 'T's even tho some still drive on the road.

    ethicalpaul
  • Jamie Hall
    Jamie Hall Member Posts: 24,856

    Not saying the modern digitals aren't good. They are, and have a lot of features people really like — and particularly with faster responding heating systems such as forced air or many heat pumps they really can save you energy. Maybe even enough to pay for them.

    They are reliable, too — in the sense that while they are working, the do work. However, I doubt we will see too many pushing much past the 20 year mark…

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    delcrossv
  • HomerJSmith
    HomerJSmith Member Posts: 2,635
    edited October 18

    @Jamie Hall, I guess we will find out in 20 yrs , I won't be around to see it. Of course, if there's a 3rd World War they will only have to last for 15 min.

    P.S. I have some digital White-Rogers (Emerson) thermostats that are pushing 20 yrs.

    delcrossv
  • Jamie Hall
    Jamie Hall Member Posts: 24,856

    True enough, @HomerJSmith . Be an interesting 15 minutes, though…

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    Can I set the differential on my Honeywell Chronotherm? What is ideal?

    Thermostat Setpoint and Differential:

    • Thermostat differential refers to the temperature range at which the thermostat calls for heat. If the differential is too narrow (e.g., 0.5°F), the boiler will cycle frequently. Setting a wider differential (1-2°F) allows the boiler to run longer and achieve a more efficient cycle.
    • Example: If you set the thermostat to 70°F with a 2°F differential, the boiler will turn on when the temperature drops to 68°F and turn off when it reaches 70°F, allowing longer, more efficient cycles.

  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    I've seen the same analysis applied to A/C.

     and you lost all your savings when you turned up the thermostat to recover from the lower temperature. I have looked at this and did some unscientific tests on my own home back then and came up with this:

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    AC is more complicated. because there is Latent heat involved. If you let your room temperature increase, ther will be room in the air for more dissolved water vapor or humidity. depending on how tight the envelop of the building is, that humidity can encroach very quickly. Then your AC needs to work hard to remove the humidity before the temperature drops.

    So I believe that keeping the temperature on the AC at a constant level is best.

    Heat… over 4 hours to start saving anything.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    CoachBoilermaker
  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    So, if I want overnight/away at work to be 60F, I set blue to 60F

    and home at evening/weekend at home to be 67F, set red to 67F ?

    Then I must set the blue/red clock thing?

    And weekend, I need to modify for weekend daytime by over riding the blue set back to be pushed together with red at 67F?

  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    As long as you don't need WiFi control of your system, and you can compensate for the accuracy of the calibration, you have a superior thermostat for a boiler like yours. Don't get rid of it!

    @EdTheHeaterMan

    Why is the old Chronotherm thermostat superior for an oil/steam boiler ?

  • ethicalpaul
    ethicalpaul Member Posts: 6,667

    Ed can answer what he was thinking there, but I will say that I think he was being a little hyperbolic.

    Modern thermostats, even smart thermostats, have different settings for different kinds of heat. They will have a setting for forced air, then one for radiant, and maybe a different one for heat pumps.

    The biggest single variable that I have seen that these settings actually change is the "swing" of the thermostat—the difference between when it turns on and when it turns off for a given temperature setting.

    So if you set a thermostat for 70, it might have a swing of one degree for forced hot air, so it might turn on the heat at 69.5 and turn it off at 70.5.

    This small of a swing doesn't work well for radiant heat like steam or hot water, so a lot of thermostats will have a swing of like 2 degrees for those…the heat would come on at 69 and turn off at 71, for example.

    Some thermostats, especially old ones seemed to describe this as "cycles per hour" but I was always skeptical of the accuracy of that. I think they used that language just to make it easier for homeowners to understand. The thermostat had no way to know how many cycles per hour it would be—there are too many variables such as heat loss, outdoor temperature, size of heating appliance. There is a thing called "outdoor reset" where the thermostat knows the outdoor temperature, but lots of new and old thermostats don't have that.

    So if you want to replace your thermostat, look in the manual of the one you're looking at and see if it has a setting for the type of heat. It might not name steam specifically, but the "hot water radiant" setting is close enough.

    NJ Steam Homeowner.
    Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
    See my sight glass boiler videos: https://bit.ly/3sZW1el

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    @ethicalpaul has a great explanation of many of the new thermostats. Ability to select cycles per hour and system type. And Paul has a mind for research and finding the answers to things, so to have a better understanding of them.

    Paul also has one steam boiler in his home for reference. Others like HVACNUT and Homer Smith, along with myself have had experience with many different customers, so many different systems of all makes models and heating media like water air and steam. With that information in mind, the Honeywell Chronotherm uses the temperature sensing apparatus of the classic Honeywell T 87F round thermostat. That is the part of the thermostat that I am referring to when I suggest that you keep the one you have. The perfectly balanced weight of the mercury switch on the bimetal temperature sensing element is one of the most accurate devices ever invented.

    When it is coupled with the heat anticipator, properly calibrated for the type of system it is connected to, the temperature in the home stays within a 1.5° to 2° comfort zone. The heat anticipator is actually a small resistance heater that is adjustable that provides a false amount of additional heat to allow the thermostat to shut off early in anticipation of the residual heat from radiators to overshoot the desired setpoint temperature. With a gravity, hot water system or a steam system, when the thermostat is satisfied and the burner stops operating, the heat in the radiators does not stop immediately. There is a rather long time delay from the point the burner stops operating until the heating elements in the rooms actually start to cool down. The mechanism inside the T 87F round thermostat which is also in your chronic therm thermostat is uniquely designed to keep your home comfortable with the type of system you have.


    Just one man’s opinion

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    ethicalpaulPRR
  • Jamie Hall
    Jamie Hall Member Posts: 24,856

    And I completely second @EdTheHeaterMan 's comment!

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EdTheHeaterMan
  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    I still don't really get why replacing an old Chronotherm is such a bad idea.

    Cost? A new thermostat is $15 to $100.

    Reliability? Are new ones THAT bad?

    Anticipator? Seems easily programmed into the logic board. Temp set to 68? Shut off at 67.

    Swing? Seems easily programmed into the logic board. Temp set to X? Start boiler at X-1

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380
    edited November 3

    What are your goals when considering the new thermostat? This may give us (me) insight into your ideas. ✔️New for new's sake. ✔️better comfort control, ✔️it looks old, ✔️it is out of calibration, ✔️other?

    If it is a comfort thing, then perhaps we can help you get the calibration and heat anticipator setting dialed in, to your system and your comfort level. If it is just cosmetic, then you will need to research a thermostat that will do the job with your system, to minimize short cycling and provide the proper software algorithm to copy the T87F mechanical process. If it is just for a hypothetical discussion. then I will refer you the those music lovers that prefer to listen to their music on 12" vinyl as apposed to MP3. I personally don't heat the difference on my 4" round speaker in my AM transistor radio I got when I was in high school. It has been tuned to WIBG 99 AM since 1972. Love those Beach Boys

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • pecmsg
    pecmsg Member Posts: 5,291
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    Big Furry Monster?

    Brute Force Method?

    Business Financial Manager?

    Bull Freakin' Manure? (🐂💩)

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    HomerJSmith
  • Jamie Hall
    Jamie Hall Member Posts: 24,856

    Well, @CoachBoilermaker , there are two reasons to be happy with the Chronotherm — and several to be unhappy with a digital replacement.

    The first reason is that unless you physically damage it, the Chronotherm will keep working reliably, every time.

    The second is that the approach to anticipation and minimizing space swing or deadband which it uses is also utterly reliable and simple, and keeps working.

    You are quite right, of course: given sufficient computing power in a digital thermostat you can accomplish much the same thing. The problem to be solved is not, however, quite as simple as it looks — as the necessary time offset to account for the lag in the system after the boiler shuts off or the lag in the system when the boiler turns on is not a constant, but is affected by room heat loss rate (and hence exterior factors like temperature and wind) as well as the physical properties of the radiation in the space and even the length of time of the previous cycle, if that didn't completely fill the radiation.

    Thus unless your digital thermometer not only incorporates a temperature sensor but also a rate of change thermometer and a current set error algorithm, it's always going to be at best an approximation. For better or worse, and to the intense irritation of the computer minded, an anticipator, once set for the space and the equipment, does all that without further attention. Giving, potentially much closer control.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Jamie Hall
    Jamie Hall Member Posts: 24,856

    Is that the comment on those who prefer 12" vinyl? Um… well… yeah. I do have a decent collection of CDs, and I do listen to music over the internet… but… I have about 30 feet of LPs and two turntables for them — and a third turntable for the 6 feet or so of 78 rpm 12" and 7" records… does that make me old? I suppose…

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    pecmsgEdTheHeaterMan
  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    Thanks for the replies.

    I guess I have no real justification to replace the Chronotherm yet. Knee jerk was that it's old and obsolete, and newer Wifi programmable would be better and more modern looking.

    I need to learn how to use this thing. Open it up. Verify anticipator setting. Replace battery and set clock. Learn to use red/blue pins to toggle set back.

  • CoachBoilermaker
    CoachBoilermaker Member Posts: 347

    I don't get your logic. The Chronotherm has a manual anticipator setting. Why can't digital also have the same thing?

    You are quite right, of course: given sufficient computing power in a digital thermostat you can accomplish much the same thing. The problem to be solved is not, however, quite as simple as it looks — as the necessary time offset to account for the lag in the system after the boiler shuts off or the lag in the system when the boiler turns on is not a constant, but is affected by room heat loss rate (and hence exterior factors like temperature and wind) as well as the physical properties of the radiation in the space and even the length of time of the previous cycle, if that didn't completely fill the radiation.

    Thus unless your digital thermometer not only incorporates a temperature sensor but also a rate of change thermometer and a current set error algorithm, it's always going to be at best an approximation. For better or worse, and to the intense irritation of the computer minded, an anticipator, once set for the space and the equipment, does all that without further attention. Giving, potentially much closer control.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    Do you currently set the thermostat to a lower temperature at regular intervals? Steam boilers can handle that set back and recovery. But need to know that you should set back about 5° and for at least 4 hours or longer to actually see any savings. 8 hours would probably be better. Most folks leave their thermostat at one temperature and forget about it

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?