Select and Install Thermostat

TomH42

In 2011 our boiler short cycled quite a bit and the help on this board was tremendous. I was instructed on how to clean the pigtail and the pressuretrol which got us through the last two winters.



To start this season my wife called a professional to check the system. I now know he did not clean out the pigtail (I did that a week ago and things have improved on that end) and messed up our thermostat.



The system now cycles on and off every 2 minutes if we are calling for heat to remain stable. This never used to be a problem. Steam is not getting to the top floor unless we call for a considerable increase in heat throughout the house.



We will ask for help on selection and installation of vents for radiators in a couple days, as well as how to determine radiator energy input/output to determine size of boiler. Today I am looking to determine how hard it is to install a digital thermostat (no programming needed, just a reliable digital unit).



What brand/model should I look to? In another thread here someone mentioned that Honeywell makes a digital thermostat that works well with steam. If anyone has a model number that would be great.



Is it very intricate to change out a thermostat? Where is the best place to locate thermostats at a reasonable price?



Here is photo of the current thermostat.



Thanks for the help.



Tom

Jamie Hall

Wonders never cease...

How can someone check a system and mess up a simple thermostat?



Oh well...



If it's a two wire thermostat -- most are -- I would suggest almost any of the Honeywell VisionPro series.  They come in a variety of flavours, and a variety of prices.  The one I use is a CT8602 and works just fine.



If it is two wire, which it probably is, it's not hard to install.

TomH42

Two Wire?

Thanks Jamie. I will research HW VisionPro series after I ensure it is a two wire setup. Is there an easy way to determine if it is a two wire unit? I assume I take off the face. Is there something else to look for?

Rod

Other Possibilities

Hi- Are you sure it's the thermostat causing the problem? If you have worked on the pigtail recently it maybe that the pressuretrol is the source of your problem.  There may be some debris in the fitting where the unit and the pressuretrol screw together. I would check my pigtail again.  Another possibility is that the guy that worked on the boiler may have screwed up the settings on the pressuretrol. 

If it is an older unit (mercury type), it's very important that it is perfectly level. (check it with a bubble level)   You need to orient the pigtail so that standing in front of it you don't see the loop (see attached diagram) otherwise the expansion/ contraction of the loop will move the control box out of level.

- Rod 

Rod

Thermostat/Contoller

Hi- If it is two wire, you can jumper the wires temporarily which will turn on the burner. If the burner then continues cycling "on and off every 2 minutes" you know it is the controller rather than the thermostat which is causing the problem.

- Rod

billtwocase

what is the amperage setting?

it is probably .2, try .4     Some digital thermostat don't have a CPH adjustment, and will run all too often also. Where is the thermostat located? Is it level? Sorry, but a genuine T87 is a good thermostat, unless you want a program.

billtwocase

also

that is a mercury thermostat, and needs to be disposed of properly. It is a 2 piece unit to remove. 

TomH42

Pressuretrol level?

The pressuretrol is not level. The pigtail loop is also facing the wrong way. The pressuretrol was installed that way 18 years ago.



So maybe my resources will not be spent on a thermostat yet.



OK, so what is the best way to at least get the Pressuretrol level?



Changing the profile of the pigtail may be above my paygrade! I do know that pressuretrol has worked well through the years when clean.

TomH42

Controller

When the request for heat is significant, (8 more degrees than current reading), the boiler will operate continuously until pressure cut off engages. Which by the way is much higher than the setting on pressuretrol. Setting at 1.5 and it is cutting out at 4.5. This may have something to do with a pressuretrol that is not level.



For now, step one seems to be leveling out pressuretrol.

TomH42

GoodThermostat

OK, I will not move in the direction of new thermostat yet. Especially if the one I have is a stable one. Thanks for the reminder about disposal.



Also, the thermostat is basically in the middle of the house on an interior wall.

BobC

Pressuretrol may not need leveling

Your pressuretrol looks like it probably has a microswitch inside and not a mercury bulb. If the pressuretrol does have a switch in it leveling is not necessary.



If you take the front cover off the pressuretrol the white dial inside should be set to one, that would let it trip out between 1.5 and 2 PSI. Pressuretrols are not known for their accuracy so it could be tripping higher than it should but check on the setting of that white dial inside to see if it is set one one.



If adjusting your thermostat gets the system working better you should be all set but it may take some experimentation to find the right setting. I did replace my thermostat a few years ago with a Honeywell RTH6450 and that does have a setting for steam and has worked well on my system. I bought in on Amazon and it was not expensive.



Bob

Rod

Pressuretrol Settings

Hi - Do you have working pressure gauge? If so at what pressure does the burner cut off  and at what pressure does the burner cut back on again?  I couldn't see what the settings were in the picture you posted.  For residential steam systems the maximum pressure (cut off) should be 2 PSI and the cut in pressure should be 1/2 PSI. I couldn't tell the model from the picture but most of the pressuretrols are subtractive so the higher setting is 2 PSI and the differential setting is 1 1/2 PSI.  With steam systems the lower pressure you can get them to run the better they operate.

 

  While I think of it I might mention that if you don't have it already there are some very good books on residential steam heating in the Shop section of the website. I would recommend that you start with a book called "We Got Steam Heat!"

http://www.heatinghelp.com/products/Steam-Heating-Books/25/61/We-Got-Steam-Heat-A-Homeowners-Guide-to-Peaceful-Coexistence

It's written for the homeowner new to Steam Heating and in an evening or two will advance your knowledge of steam heating light years ahead. It the book most of us who are homeowners started on. This book will pay for itself very quickly!!!



At this point let's not worryabout the controller being level. If it has worked this way before it 's probably okay now.  Let's check the controller settings and if necessary make adjustments. The screw on top moves the pressure up and down.

If you remove your control again to check the pigtail you might want to install a pipe union between the pigtail and the controller as that makes it much easier to take off to check and clean the pigtail.

- Rod

Edit: It's not a mercury switch so being perfectly level is not that important

TomH42

Open pressuretrol

Hi Bob. Here is a photo of the opened pressuretrol. I do not see a mercury bulb. Can you identify a microswitch?



If it has a microswitch, is the direction of the pigtail a concern?



Also, do I need to slightly adjust the white dial, moving the 1 to the right?



Thanks.

TomH42

Settings photo

Hi Rod,



Setting photo is right above your last post. I think the settings are pretty standard. The pressure gauge is probably too big and not precise for low pressure steam heat. However it is all we have for now. The pressure has been shutting down the boiler at about 4.5 psi. It kicks back in at .5 approximately.



The largest concern continues to be stopping and starting when the system is near the desired room temperature.



I do have the book which is informative and necessary for anyone who has steam. Outside of low water cut off (and adding water) I knew nothing about the system. Last year I added a main line vent and learned to clean pig tail. Who knows what the new year will bring!

Rod

Pressuretrol

Hi Tom- Your Pressuretrol is additive which means the top screw needs to be adjust to the minimum setting and the inside white wheel to 1 1/2 .  If your pressure is actually rising (gauge is accurate)  to 4 1/2 PSI, that is way too much. Building pressure uses more fuel!

I've attached what I believe is the manual for that Pressuretrol.

- Rod

BobC

microswitch

Rod is right your pressuretrol has a microswitch (brown with two terminals at the top) and does not have to be level to work correctly.I have one just like yours as a spare and that white dial should be moved as far to the right as it will go. Don't touch the wires on that microswitch they have 120v on them.



Your gauge might not be very accurate at the low end so don't take it's reading as gospel, at some point you might consider adding an auxiliary low pressure gauge so you will know what is really going on.. Check all of your radiator air vents to be sure they are working and that they shut once steam reaches them.



Bob

TomH42

Moved White Dial

Thanks fellas,



So the white dial has now been moved as far right as it can go. I will assess the cut off's due to pressure for the next few days/cycles depending on what comes first. I would love to have a low pressure gauge. For now, not feasible.



Air vents on each radiator next, but for now, one problem at a time.