problem thermostat...

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  #1  
Old 12-02-02, 09:29 AM
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Question problem thermostat...

...or problem owner?

This will be my 1st winter in a house with a one pipe steam system. A problem I've been experiencing is that if I set the thermostat where I want it (around 68 degrees) the heat will kick on before the thermostat reaches that level (when it reaches about 70 degrees or so) and stay on long enough to raise the temp a few degrees, but not long enough to heat the radiators a significant amount or warm parts of the house that are significanly cooler than the room where the thermostat is. If I set the thermostat to around 65, the heat will not kick on until the temp drops to 65, but then that means waiting until the house is uncofortably cool for the heat to kick in. At least with the thermostat set lower the heat will stay on longer and significantly heat the radiators.

The thermostat is a Honeywell and has a mercury switch. It's not one of the round ones, but has a sliding bar at the bottom. I removed the cover, but there was no further identifying info. There were 2 wires visible, both white. I refrained from removing it from the wall for fear of accidently disconnecting something and not being able to reconnect.

Is this just a matter of me having to find a happy medium on the temp adjustment or is this the sign of a thermostat that could use replacing?

In a probably unrelated note, on a particularly cold/windy night over the weekend my wife set the thermostat up to around 75. I was awakened about 3 hours later with steam jetting out of all of the adjustable airvents (the automatic vents were fine) and the house uncomfortably hot. I rushed down stairs to the thermostat and set the temp back down to a more normal level (I was too groggy to note what actual temp the thermostat was registering). I went into the basement to make sure that the boiler was shutting off and I noticed that the steam pressure had been at least 5psi (normally the needle barely registers any pressure). Should the pressure have gotten that high? Since I don't know what temp the thermostat was reading as actual temperature I don't know if it had failed to shut down the boiler after reaching the desired temp, but it sure seemed that way. Also, shouldn't the boiler shut down if the pressure gets so high that steam is jetting out of the air vents at such high pressure you can hear it in another room?

Sorry this was so long, but this is all new to me and I want to get potential problems before they become significant issues. Please excuse my ignorance on the subject. I've looked at the "steam problems?" section of "heatinghelp.com", but thought these problems (real or imagined) seem like they might be more thremostat related.

I appreciate any help you can give to a rank novice.

Thanks,

matt
 
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  #2  
Old 12-02-02, 04:18 PM
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thetick24603:

I'm quite sure the answer to your specific steam questions can be found on HeatingHelp.com.

The thermostat problem I may be able to help.

Inside the thermostat is an adjustable heat anticipator.
It has an adjustment lever that has some numbers and the terms "longer - shorter.
This controls the amount of time the heat stays on and off.

If you move the control towards longer it should do a better job for you.
Other things that can affect the stat are drafts, being installed on an outside wall or a burned out anticipator.

Check this out and let us know.
 
  #3  
Old 12-02-02, 05:18 PM
fesjr
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GregH is rtight about the anticipator, but it must be set according to the manufactures recomenfdation. This is found in the boilers owners manual.
The fact that steam was coming out of the adjustable vents means they need to be changed. They should close when the steam touches them.
You pressure troll on your boiler could be bad or set to high. It should be set to 1/2 lb (up down slider, adjust with flat head srewdriver), with a 1 differential( white knob). This will cycle the boiler between 1/2 lb and 1.5 lbs untill thermostat is satisfied.

Hope this helps.
 
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Old 12-03-02, 07:08 AM
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what I found...

Ok. So I'm either daft or didn't do a good job of identifying my thermostat. I removed the cover again this morning to look for the adjustable heat anticipator. I didn't find anything approximating what you described. What I did find was 2 springs. A little tightly wound one attached to the actual temperature needle and a larger one attached to the lever used to adjust the temp setting with a mercury switch on top of the spring. (Of course by spring I dont' mean a coil spring like you'd find on a garage door, but a spiral spring that's tight in the middle and gets more loose at the outside layers. I'm sure you know that, but I wanted to cover my butt incase they're not actually called springs.) I also was able to make out some writing that I didn't notice before because it was largely behind the large spring and is pretty faded. The markings were as follows:

-Powerpile Only .75 DC

-FF1 TS88D 1069 1

Again the thermostat is a Honeywell and does not appear to have any date markings.

As for my boiler and the steam pressure issue. I removed the service cover from the boiler and on the pressure troll (also Honeywell) the cut in was set at around 2.5 psi on the sliding indicator. There were two screws, both standard slot. One on top and one on the face. There was no indication of what the cut-off/out pressure was or what the interval was for cut-off/out. It had the following markings on the side:

PA 404A 1009 1

Incase it helps the boiler is a National US boiler no. 109-5, steam 300 sq ft. , 120,000 btu input, 96,000 btu output. It had the notation that Max working pressure is 15psi. We've been told the boiler is 10-15 years old, but we do not have the owners manual or proof that this is the actual age of the boiler.

I don't know if this helps.

Thanks for any further help/advice you can provide.

Matt
 
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Old 12-03-02, 11:26 AM
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Powerpile is a good clue!

thetick24603:

What you have is a self generating pilot assembly.
Havn't worked on one of these in a long while.

Your pilot assembly generates a small current to enegize the gas valve. There would be no 24 volt transformer to run the valve.

I believe the anticipator in those stats are fixed and cannot be adjusted.

The anticipator in yours could have burned out. It is just a very fine wrap of wire that generates heat within the thermostat housing to control the cycling.

People sometimes won't believe that stats don't work without the cover in place.

They are not that expensive. I would replace or have it replaced and the cycling problem should go away.
Just make sure it is a powerpile stat, as a 24 volt one uses a different anticipator range.
 
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Old 12-03-02, 11:53 AM
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so then...

...would I be able to replace it with a programable thermostat? From your tone it would seem like this is an antiquated type of thermostat and a replacement might not include such conveniences as the ability to program different heat settings for different times of day. Also, would this type of self generating pilot have anything to do with the pressure cut-in being set at 2.5 psi?

While my system may not be functioning ideally, it's still functioning reasonably well and I wouldn't want to create a larger problem by trying to fine tune my system by dropping the cut-in level. In other words, if these two things are related (the thermostat and the pressure setting) I don't want to upset some balance that the previous owner (or pro hired by her. She wouldn't know an outlet from a lightswitch.) had achieved between the two. I guess I am just trying to decide where the line between helping and hurting is.

Thanks for the 411. I appreciate any additional info you or someone else might provide.

Matt
 
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Old 12-03-02, 04:10 PM
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thetick24603:

The problem with the thermostat and the boiler pressure are two totally different problems.
I have little experience with steam heat, so I'll stay away from that one.

The job of the thermostat is to control the on/off cycles of your heat.
If the temperature swings widely the thermostat would need to be changed.

If you purchase your replacement thermostat from a specialty heating store or a heating contractor you would be more satisfied with the results.
It is rare to find a clerk at a department store that would know anything about this.
 
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Old 12-03-02, 06:29 PM
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thanks...

Good to know. I appreciate the honesty. What you don't know is just as important to me as what you do. At least I can begin shopping for a new t-stat while it's not yet a serious problem and just an inconvenience. Plus I need to get to a heating supply store anyways for steam pipe insulation and this gives me another reason to get off my duff.

thanks for the info!

Matt
 
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Old 12-03-02, 06:49 PM
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thetick24603:

Check out this site:

http://www.heatinghelp.com/steam_problems.cfm

Lots of good reading on steam systems.
 
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Old 12-04-02, 02:04 PM
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Perhaps we could take some time to discuss some issues. On a conventional thermostat with a heating anticipator, the anticipator resistor is wired in SERIES with the thermostat heat switch. Translation- if the anticipator is burned out then the heating circuit will be open and the heating unit will not operate. Now, the heat anticipators job is to fool the thermostat into thinking [pardon my personification] that the space temperature is warmer than it really is. Typically, a gas or oil furnace will continue to put heat into the conditioned space after the burners shut off. This is because the fan is still running umtil it reaches the cutoff temperature on the fan control. [on newer furnaces, the board or module controls the fan, usually by time] The heat from the heat anticipator resistor causes the t-stat to shut the burners off a little early to prevent overheating the space. The thermostat you describe is in fact a Powerpile or 750 millivolt system thermostat. These systems operate on 750 millivolts or 3/4 of a volt. The power to operate the system comes from the Powerpile generator which is the thermocouple in the pilot burner flame. Standard safety thermocouples generate 30mv and a Powerpile generator is a number of thermocouples put together designed to produce 750mv. The idea is that you will still have heat if a storm knocks out the power to your house. [that is so long as gas is available] Because these systems operate on such low voltage, Powerpile thermostats do not have heat anticipators. A heat anticipator resistor would add too much voltage drop to the circuit. That helps to explain why your thermostat misses the mark. Another thing to check is to make sure the thermostat is level on the wall. You can't directly install a programmable thermostat on a Powerpile system. I imagine you might be able to have a programmable thermostat operate an interface relay wired in series with the Powerpile system. IOW- the relay contacts would take place of the Powerpile thermostat. Actually, to have the best of both worlds, you could use 2 relays. Relay 1 would keep the Powerpile thermostat out of the circuit so long as there was electricity to keep the relay pulled in. Relay 2 would operate the boiler under the command of the programmable thermostat. If a Winter storm knocked out the electricity for a few days, control of the boiler would automatically revert to the Powerpile thermostat. You would have to install a 24 volt transfomer in order to make this hookup work, but I think it would be ideal. Now, the PA404A is a pressuetrol that is intended to act as a high pressure limit for the boiler. IOW- the thermostat operates the boiler and the pressuretrol shuts down the burner in case the boiler pressure is too high. They are wired in series with each other. If the setting says CUT IN, then you have a pressuretrol with additive differential. The setting on the scaleplate is the pressure at which the boiler will cut in. The cut out pressure will be the cut in, PLUS the differential. The differential dial is inside the control. For example, if you set the cut in at 2.5 and the differential at 4, then the boiler will cut in at 2.5 and cut out at 6.5. Remember, the thermostat operates the boiler and the pressuretrol is a high pressure limit safety switch. At http://hbctechlit.honeywell.com you'll find literature on both the thermostat and the pressuretrol. Just type in your model numbers and hit search. You can also type in programmable thermostat to look for various models. You can have the installation instructions available while planning a project. I use a lot of Honeywell products because it's so easy for me to download the literature I need to figure how to accomplish a job. At any rate, the method in my madness is to give you some background to understand your system better. Hope this helps.
 
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Old 12-04-02, 04:58 PM
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bigjohn:
Thanks for the clarification.
I checked out Honeywell's site before I posted and it showed the TS86 powerpile stat as having a fixed anticipator.

thetick24603:
The simplest thing for you to do would be to replace the thermostat with the same type. Honeywell make a round one and a rectangular one. They both work the same.
You could use a programmable thermostat with a transformer and a relay.
A heating contractor could do this for you.
 
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Old 12-04-02, 06:47 PM
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Yes sir, it's right there in black and white. First time I've seen a Powerpile stat with an anticipator. It would have to be a very small amount of resistance. Thanks.
 
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Old 12-05-02, 07:58 AM
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Thumbs up outstanding...

Big John comes through with big-time info!

Thank you for taking the time to explain what type of thermostat I have and how it would/wouldn't work inregards to a replacement thermostat. Too bad I can't disconnect the old one and just "plug in" a new programable one, but I suppose thems the breaks and it is reassuring to know that my heat won't go out if the power does. I especially appreciate the direction to the Honeywell site for on-line manuals/documentation. This is exactly what I need! Now I can take the time to learn about it/trouble shoot without having to pester people here all the time. Now if only I can find a similar site to get info/users manual for my National U.S. boiler I'll really be cooking with gas (sorry about the pun)

The info about the pressuretrol is also very useful! I'm a reasonably smart guy, but between my relative youth and inexperience with steam heating I lack a lot of basic knowledge on how the system and its various parts work both individually and in relation to one another. I understand the basic physics of how a steam system works, but not necessarily how the various parts of the system work, so I appreciate you taking the time to explain them and then re-explain them in a different fasion so that between the 2 sets of info I can gleen enough for it to make sense to even me.

Thanks again, you guys are the best!

Matt
 
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