Temperature Control


Old 12-21-02, 01:49 AM
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Thermostat? - Too cold - Gas- Robertshaw

I've labeled this thread confusingly, because no matter how I approached my search in my quest for answers, I always ended up with too many results and I hope that by making the keywords obvious, we may be able to help others in the end.

My wife and I bought a fixer-upper a couple of months ago which she jokingly refers to as a museum of heating systems; The woodstove works fine and I haven't gotten around to the fireplace, yet and because I need to rewire, I haven't tried the built-in electric space heaters in the bathrooms; But, I did try one of the electric baseboards one cold night only to find that it wouldn't heat, so after looking through my repair library and checking a couple of things, I decided that our new-fangled electric space heater would supplment that room just fine and never tried to start any of the others, throughout the house.

But my "problem" is with one of the thermostats which controls one of the wall-mounted, six and a half foot tall, Perfection brand natural gas space heaters which was manufactured in 1980. As far as I can tell, the heater works fine; But I oftentimes complain that it's cold and I check the thermostat to see if my wife had reset it before the burner lights and the heater kicks on.

This evening, because we were working in the Family room setting up the Christmas Tree, I had the same complaint and when I looked at the thermostat, I noticed that though it was set on 70, the thermometer actually looked to be closer to 61 or 62; So, I touched the control slightly and the heater kicked-on; I, then went to my computer to search this forum which brings me to his moment in history.

Each Perfection heater has it's own thermostat and nothing other than the gas line connects the units as far as I can tell; Though, I've been busy winterizing and fixing the plumbing so the place would be livable and I haven't gotten around to mapping the electrical system, yet.

The heater in the living room has what appears to be a more modern (relatively) "Robertshaw" thermostat and that heater kicks on somewhere in the neighborhood of 65 to 66 degrees.

The heater in the Family Room is also has a "Robertshaw" and under the cover, I see that it's 30 Volts and it has two lines which appear to be product numbers, though they aren't identified as such. The topline says D87005 and directly below it is stamped, 87006.

It should also be noted that this particular thermostat has two switches underneath, one to go between heat and cool and the other supposedly to control the fan; Though, this has no bearing on the problem at hand; I just include this info primarily for idenification purposes.

There is an evaporative cooler for that room which I tested via the buttons on the unit and there's another thermostat in the room which may go to the evaporative cooler, or it could be leftover from the floor furnace which was removed when they put down the carpeting; I'm not sure, but I know it has nothing to do with the space heater and once again, I only am including this info as a possibly alternative method to control the cooler and to stress that the cooling side of the problem thermostat may not be connected to anything, whatsoever.

Also from reading previous threads, we only started getting into the teens recently and the "problem" has been more noticeable, lately; Plus, when I pulled the thermostat cover off to get the model numbers, I noticed the heater more readily kicked-in and from looking at the thermometer on the aforementioned, I don't know what it's for thermostat, it appeared to be 67 degrees which would correspond somewhat to my touching the problem thermostat up to 71 before I pulled the cover.

I let the heater go twice while typing this and both times, the other thermostat read pretty close to 67 and then I replaced the cover just to make certain that I hadn't bumped it up while getting the model numbers; So, it appears that it may work correctly with the cover removed.

And finally, under the cover and hidden from view is a slidey thing that is numbered from 2 to 10 and it's set on 4; Once again, I don't know if this has any bearing, but I'm including the info in case it matters...

Any suggestions would be greatly appreciated.

Thanks in Advance;

Last edited by magister; 12-21-02 at 02:33 AM.
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Old 12-21-02, 06:40 AM
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Smile Hmm.............where to begin?


Firstly, don't be concerned about the actual setting of the thermostat in relation to the room temp. If the stats are old they could be out of calibration.

The "slidey thing" is the heat anticipator, which controls the on/off cycling of the stat.
The fact it works better with the cover removed is a clue.
There should be numbers which relate to the milliamp settings and an arrow that says shorter - longer.

There is a certain setting required based on the gas valve or relay's requirements.
Barring that you can move the anticipator and use trial and error to get it right.
Try moving it to shorter or a smaller number.

To help trace out the different controls you could look at the number of wires connected to the thermostat to see how many are actually connected to the thermostat.
I will on occasion use a heat/cool stat on a heating only application if it's all I have and the customer doesn't want me to come back.
Old 12-21-02, 08:12 AM
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Lightbulb Additional Possible Problems & Solutions

Hello: Magister

May be the wrong type of thermostat for that heater. Method for determining. If the wall heater in question does not have any house electrical current supplied to it for running a heat distributing blower fan, etc, the heater does not need a low voltage thermostat.

It needs a milivolt T-Stat. A pilot generator {PG} will be used to produce the low voltage DC current needed to operate the gas valve and the thermostat.

The PG is a round very low voltage dc electrical producing element in the pilot assembly with flames encircling it. PG's wear out slowly over time and as a result produces less than it's full rated electrical capacity.

Do not be concerned about the PG's rated capacity, testing it's current volt capacity & other concerns, etc. Simply based on the heaters age, replacing the PG may be required & the solution to the problem.

The pilots flame must be all blue and fully encircled around the PG. Lint or dust in the pilots assembly will not produce pilot flames hot enough to heat the PG to allow it to produce it's rated dc current. Be sure the pilot flame is all blue and the PG glows a bright cherry red color. If not, clean the pilot assembly.

Another possibility could be the type of thermostat. If it's a mercury liquid filled bulb type, these usually last years and remain accurate. Cleaning the wire contacts may resolve the problem.

If the T-Stat has contact points, the points may be worn out, pitted, damage or dirty, etc. Replacing the T-Stat resolves the problem.

If you need further assistance, use the REPLY button after attempting the correctional method or methods offered.

Regards & Good Luck, Forum Host & Multiple Topic Moderator.
TCB4U2B2B Company Enterprises. Energy Conservation Consultant & Gas Appliance Diagnostics Technician.
Old 12-21-02, 09:49 AM
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Thanks for the response, Greg;

But first of all, I do kinda have to worry about the stat's setting in relation to the room temp because the heater is kicking-off pretty close to the right temperature, it just lets it get too cold before it comes on, initially.

I thought the "slidey thing" may be the anticipator which I read about in a previous thread and that's why I included it in my description, but mine isn't labelled "shorter" and "longer"; Instead, it has the numbers with the spacing between the settings further apart for "2" coming closer together as it gets towards "10", so I couldn't be sure that it was the same thing.

Also, I can't swear that it actually works better with the cover off; That was just an impression that I got last night, but later on I got the impression that perhaps it would get "stuck" in the off position and by bumping it up slightly, I freed it. I'm still not sure which is correct; It's simply difficult to tell without knowing whether or not this second theory is even possible and devising some kind of test to measure it's accuracy.

And I understand your point about the thermostat possibly just being the one on the truck; Though, I find it doubtful that a tech has ever looked at the stat; The house was built in '54 by two brothers for a third and it was maintained by these same brothers for the third's widow; Most everything in this house came from the local "True Value" and I figured that this was simply the only stat in stock when they shopped for a replacement. But I included the info in an effort to prevent someone from simply volunteering that I had the wrong thermostat.

And thanks for the response, Tom;

According to the manual, the unit shipped with a wall-mounted thermostat and it includes instructions for locating it and wiring diagrams for connecting it to the house current and the diagrams make specific reference to the unit's large fan, or blower.

It does appear from the diagrams that it may have shipped with a 24v stat; At least, that's how I interpret the diagrams and this unit which looks to be a replacement is labelled 30v; But, since the other heater/stat combination is also a 30v, though it is clearly marked on the inside "Heat Only"; I figured the difference between 30v and 24v must not be important, or I'm misinterpreting the diagrams which could easily be true.

I do know that the unit shipped with a stat, but all I have is an antiquated part number and a photocopied manual which isn't the easiest thing to read when it comes to schematics. Plus, the merged and possibly re-merged company has already expressed ignorance when it comes to heaters as old as mine and the part number from the photocopied manual doesn't come up in a search of their reorganized company's site. (A110407-G1)

And for Greg, Tom or any other expert;

The manual makes no mention of the anticipator, or any correct setting for it; Plus, I can't find any manuals on the robertshaw website.

But unless I can replace this stat with an overkill of a programable, I'd prefer to try and maintain or work with one that I already own; I plan to rip out all of the evaporative coolers and antique heaters this summer and replace everything with a central unit after I've got the solar shingles on the roof to help defray the costs. I'd prefer to not buy a thermostat now that'll only be good for the remainder of the heating season, when I know that I'll be installing two programables, mid-summer.

But of course, if a programable will work; Then, I'd have no objection to buying it in advance of the upgrade, but unless I'm reading something wrong, I don't think it'll work with what I have; Though, I could be wrong.

Thanks again;

PS Tom;

From the manual under "Furnace Controls";

"This furnace has a factory installed Combination Valve with Pressure Regulator, 100% Safety Pilot and Manual Valve. A Wall Thermostat is also included."

I referred to the unit as a space heater because that's what the realtor called it and that's pretty much how it works; But now that I look, the manual is actually entitled; "Gas-Fired Vented Counterflow Wall Furnaces"...
Old 12-21-02, 10:28 AM
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My advice is as follows:

1. Tom_B is right. Regardless of whether or not you think the thermostat is the right one, go check and confirm the furnace is 24 volt by looking for a transformer in the gas valve circuit.

2. If you confirm that you have a 25 volt system then adjust the anticipator setting to a lower number. The range of one unit I'm looking at is from .25 ma to 1.23 ma.
The lower number will give you shorter cycles.
For purposes of testing I would set it to the lowest setting and make sure the cover is on.

If you get the same results after doing this the anticipator is likely burnt out.

The discrepancy between seeing a 24 and a 30 volt rating is as follows.
24 volts is the normal operating range of the controls.
The 30 volt rating gives the wiring catagory voltage of the particular controls you are working with.
For example when purchasing thermostat wire you must choose one with a 30 volt rating.
You cannot use say a speaker wire that may not have this rating.

I stock 300 volt rated control wiring because our electrical code allows me to put this stat wire in a conduit with 240 volt supply wiring.

Let us know how you make out on this.
Old 12-21-02, 12:35 PM
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OK - Now I'm a bit confused...

All information that I can find on any website says that the anticipator is only powered when the heater is operating and that the current heats the coil in order to fool the thermostat into thinking it's warmer than the actual room temperature; Unless I'm missing something, there appears to be no current or effect from the anticipator when the furnace is not operating and by adjusting the anticipator, one is only effecting the period of time that the burner is lit and I'm at a loss to understand how effecting the operational period of the burner can keep the room from getting too cold before the heater lights...

My two year-old has not been very cooperative thus far, today and I just found where she "melted" a whole roll of toilet paper in a bathroom sink that doesn't have any kind of strainer; So after I clear the sink and do a couple of other small things, I'll play with the anticipator setting;

But in the meantime, if anyone would like to correct my impression of the role of an anticipator or offer any other suggestions; I'd truly appreciate it and after I've played some more with the thermostat, I'll report back here with the results.

Last edited by magister; 12-21-02 at 01:04 PM.
Old 12-21-02, 02:41 PM
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magister :

Please, a thermostat is not a toy so don't play with it!

What I have asked you to check and report back on, is one way of diagnosing your problem. It is not playing.

It is the way I do it and charge people for and is almost always successful at isolating the problem.

There are other ways I'm sure , so maybe someone will be along that has a different approach.
Old 12-21-02, 03:40 PM
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Greg; No offense intended; Play is only a figure of speech;

I can see where you've told others to adjust the anticipator as a response to my problem and apparently it works; Plus, while I googled for further information about the anticipator, I've found countless other people in other forums on completely other boards giving the same advice, so obviously that's what needs to be done.

But unfortunately, it's 40 degrees outside and daylight, so the heater isn't needed as much as it is at night and because it really seems to be keeping a tighter range since I bumped it up; I'm reminded that it's an off and on problem; I've found myself complaining about the cold and checking the thermostat settings, but usually I'm checking the one in the living room and last night, I happened to notice the problem in the Family Room because we only recently started using that room. But, I really only have noticed the problem once a day, if that much and last night was the first time I attributed it to the thermostat in the Family Room because I happened to be in there with the lights on, so because that's where I was cold, that's the stat that I checked and that's when I noticed the variation;

The two heaters are far enough apart that their range may overlap a bit, but more likely and theoretically, the heat from each unit "bumps" up against the other; But nonetheless, what historically caused me to check the living room's stat may actually be atributable to a malfunction in the Family Room's stat and the cold was simply "bleeding over" into the other room.

But any way you look at it; The problem is more off and on and things are pretty much working, right at this moment; Plus, there really isn't much call for the heat this afternoon, so I'm limited in my testing; I hit the stat with some canned air and took a magnifier out to look for wear but as to adjusting the anticipator, I figured that I'd at least wait until sun goes down, if not until it once again started acting up, so I'd have a better idea if it was having any effect.

Once again, I apologize if my figure of speech offended you; I'm approaching this whole fixer-upper thing as a learning experience and in the process, I'd like to gain an intermediate understanding of the internal workings of a home and to me, education is fun; And that's also the reason for my request for clarification, I just wanted an understanding of the cause and effect, even though, clearly you had prescribed the correct course of action.
Old 12-21-02, 03:46 PM
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Your assessment of the heat anticipator operation is correct. Many gas furnaces operate with this sequence- thermostat contacts close and the burners lite. The furnace warms up to the ON setting of the fan control switch in the furnace and the circulating fan starts. The space warms up, the thermostat contacts open and the burners shut off. The fan CONTINUES to run until the temperature in the furnace cools down to the OFF setting on the fan control. IOW- the fan continues to run adding heat to the conditioned space AFTER the thermostat has shut off. Can you see how this would overshoot the thermostat setting and cause the space to be too warm? The heat anticipator adds some heat around the thermostat bimetal so that, to the thermostat, the space temperature is warmer than it actually is. The burners shut off early and the heat added to the space by the continued operation of the fan brings the space temperature up to the thermostat setting [or close enough]. Now, the heat anticipator is wired in SERIES with the thermostat switch and is only in the circuit when the switch is closed. If the anticipator were burned out, you would not get heat in the first place. If your heater has a circulating fan, then it sounds like you have power to the furnace and the control circuit operates on 24 volts. The 30v marking on the thermostat is the maximum voltage it is designed to operate on. The reason the other guys want you to check the type of control is that a lot of wall furnaces use millivolt controls, but they would not have circulating fan, they would depend on convection currents to circulate the heated air. I suppose it's possible that you have a heater with a 120 volt fan and also millivoltage controls for the gas valve, but I doubt it. If you can find a transformer in the heater, then it's definitely not a millivoltage system. From your description it sounds like you have a snap acting thermostat. They consist of a fixed contact which has a magnet around it and a moveable contact that is attached to a bimetal sensor which is usually wound into a small coil. As the temperature around the bimetal gets colder, it moves its' contact closer and closer to the fixed contact until the pull of the magnet is strong enough to pull it in and close the contacts together which makes the circuit to the gas valve. It snaps shut to prevent bouncing on closure which could chatter the controls. On some t-stats, the contacts are exposed and, on others, they are encapsulated. You could try looking to see if the contacts are exposed and are dirty or corroded. Another check is to make sure that the thermostat is mounted level on the wall. Don't just eyeball it, use a small level to be sure. What's on the other side of the wall where the thermostat is mounted? Any thing warm which could warming the thermostat? Any warm air currents inside the wall affecting operation? Check all these things, then if the t-stat still controls poorly, go ahead and replace it with a programmable. You could just buy an inexpensive one and toss it when you re-equip or buy a good one now and reuse it. One suggestion- call your local comm. college or high school that has an HVAC program and see if they could use your old heaters for their students to learn from.
Old 12-21-02, 04:34 PM
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I wasn't offended at your phrasing, it was a poor attempt at humor.

I was picturing you fixing your stat and dealing with a two year old and imagined you telling her not to play with her food................never mind.


Thanks for your input.
Old 12-21-02, 05:45 PM
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Aw for the good old days . When honeywell first came out with the T87 we were given some test one's to try. They had the little red pointer that showed the temperature there on the bottom side of the T87 and on the top side they just had some lines that you could set the pointer too.You know there wasnt one that didnt work just right. The people said they just set the pointer to the line that felt good. As far as the heat anticipator goes most of the valves have there amp draw on them and we would set it to that. You know, now that I think about it we didnt have to go back on one darn service call on any of the thermostat's ED
Old 12-21-02, 06:22 PM
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Greg; I thought you may have been kidding because the icon you inserted was named "biggrin", but since you obviously make your living fixing people's stuff; I thought I might should cover my butt because I really haven't even gotten started in my study of heating and air...

BigJohn; You called it at least as far as the "problem" stat is concerned; You pull the cover off and you see two magnets with a contact between which you have described much better than my two attempts at word pictures, so unless someone would like me to go into detail about what I see, let's just say that BigJohn described it perfectly.

As to the leveling part of the equation, I've only eyeballed it thus far; Both stats are fastened with only one screw and they both will twist when you touch them and because I now have an understanding of how the thing works with the magnets and all, I can theorize as to why the cold seemed to "move" between the rooms; It wasn't my fault, it was because the wife kept turning them down when she's home alone and I'd push them up just after walking in the door, so they're probably never perfectly level.

I'll put another screw in behind them after I've given them a trial being level; The living room stat is in a block wall and I try to avoid drilling extra holes into the block at least until I'm certain they are going to stay there...

And BTW: For informational purposes, my memory tricked me this AM; The original water heater was manufactured in 1980, but the wall heaters were actually made in '86.

After going through the heaters all day and learning a lot about how a thermostat works; I had actually started digging deeper into the subject of programables. Sometime around mid-day, I extrapolated out my utility bills (we haven't gotten a gas bill since I lit the heaters) and that exercise caused me to want to research longer than the couple of hours I spent after I got the electric bill, which was the push that I needed to light the second heater in the first place.

Though, I still haven't found the transformers; I see the picture in my book and I strongly suspect they are in the attic because after all, the wire from the thermostat goes into the attic and comes back down into the top of the heater alongside the power cable for the unit; I don't see anything in the actual heater other than the plate which is labeled "120 V. 60hz Less than 12 Amps", nor did I find anything on top of the unit other than the wires which by code should be in a box; Though, I didn't remove the big fan or it's housing which occupies the upper third of the device and there's nothing labeled transformer in the manual's parts list.

Obviously, I haven't gotten into the attic yet, either; We started the day watching a hot air balloon rally and my daughter is ending her day with a balloon glow followed by the Christmas parade, so she's been wired all day and her mama had to go back into work after being off for the past nine days and daddy has been running around looking inside of the "dangerous" heaters, so it hasn't been a picnic at my house; I can only thank the japanese and pixar for DVD's, or I wouldn't have gotten anything accomplished.

But unless I find a surprise somewhere or someone chimes in and calls me a fool; Am I safe to assume that my mid-afternoon gut reaction and my interpertation of BigJohn's post is correct and I should be able to replace these stats with any type of programable? That'll certainly reduce the tug-of-war my wife and I are having over the settings...

Thanks for all the help; I've certainly learned a lot and the next time the thing misbehaves, I'm equipped with the knowledge of what to "play" with and in the meantime, I'll level the things out and do some more research on my replacement options because once my wife hears my extrapolation of the utility bills, the battle will only intensify...

But once again; Thanks Greg, Tom and John; It was an education; And Ed, as to the good old days; Let me tell you about the stat in the storage unit which is labeled "Day & Night", but after moving a bunch of boxes and pulling the cover off, I learn that it's not an antique programable, but an obsolete brand name There should be a law...
Old 12-24-02, 01:00 PM
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Day and Night !boy thats been dead for a long time. You said your tstat had points? On old tstat that have points and not the glass bulb with mercury in it. Close the points with a business card in them and run it back an forth. This will clean them and make tthe tstat work a lot better. ED
Old 12-24-02, 04:55 PM
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Ed, I know that you remember this, one way to set the anticipator correctly for any gas valve. wrap 10 winds of tsat wire around the jaw of the amprobe insert your coil into the circuit and start the furnace, read the current draw and that is your correct anticipator setting.I've used that many many a time and rarely had a problem with a t87f or a W/R tstat.
Old 12-26-02, 02:59 AM
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Thanks Ed; The business card suggestion makes sense and I'll give it a whirl, though we seem to have "fixed" the problem by combining Greg and John's suggestion, but the business card makes sense and it won't hurt to fine-tune the existing thermostats, somewhat.

Basically, I hit the innards with some canned air and leveled both stats, but the clincher of an answer came in one of Greg's initial replies; One of the presents my wife gave me for Christmas was one of those big, easy to read outdoor thermometers. We opened presents in what we're calling the Family Room and it didn't take me long to notice that the temperature wasn't rising even though the gift was unwrapped.

This prompted me to take the thermometer into an unheated part of the house, check that it actually would move and then, I temporarily mounted it onto the wall beween the connected thermostat and the "I don't know what it's for"; Now, we know that in order for it to be 68 degrees in the family room, you've got to set the thermostat on 74 which goes back to Greg's discounting of what temperature you actually set the thermostat to and your lament for unmarked lines on the beta products.

I've decided though to replace both thermostats with new, overkill programmables probably in mid-January when I make my next monster trip to the city; Though in the meantime, I'm researching the various options and mail-order offerings including those from this website and because I'll be buying the stats in anticipation of installing a heat pump in the spring, I'm also trying to educate myself on the new-fangled idea of zones so that once I install the new stats, I'll be able to continue operation of these old heaters and not have to move them when I've switched over to a central system.

Of course, if I can figure-out an economical, efficient and reliable way to replace the old stats with PLC's, that's the way I'd prefer to go from a resale perspective; But so far, it seems that anything you can do with a PLC you can accomplish with a much less-expensive and warranteed thermostat from a respected manufacturer and any way you look at it, the PLC idea is another subject altogether...

Thanks again for the good ideas fellows and keep up the good work; I know that I saved myself quite a bit of money by consulting this forum and in case it's been awhile since anyone has said it; On behalf of DIYer's everywhere; Thanks.
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