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Troubleshooting Intermittent Firing and Adding C-Wire

nickr
nickr Member Posts: 22
edited April 12 in Strictly Steam
Single-pipe steam system in my small house, with a Utica boiler. The problem is that sometimes it'll fire when the old Honeywell CT8602 thermostat calls for heat, sometimes it won't. A technician visited yesterday and advised that one of three things could account for the intermittent firing: 1) bad thermostat, 2) bad lwco, or 3) bad pressuretrol. He recommended that I replace the thermostat (which I've wanted to do anyway) as the cheapest and easiest first potential fix.

A couple things he said during the visit make me doubt his knowledge base. First, we were discussing my main vents and he was adamant that main vents never close and should always stay open even when the steam hits them. And second, discussing my wiring, he said that c-wires are 120 volts and can't run off of the 24 volt transformer that's powering the furnace, and thus that I can't have a c-wire without major electrical work. (Current wiring setup is as follows. At the thermostat, the red is attached to R and white is attached to W. Inside the wall are the unused blue and green wires. In the basement, the blue and green terminate unused, while the red and white continue into the boiler. Separately, blue and green wires run from the boiler to a 24v transformer on the ceiling.) He also reinstalled the pressuretrol cover like he had never seen one before in his life. It was totally off-kilter and I had to re-do it once he left.

Four questions: 1) should I ask for my money back because the technician didn't know anything about anything, 2) can I use the existing wiring to add a c-wire to the system, by connecting the unused blue or green wire to the 24v transformer, 3) what thermostat should I get (I need to be able to verify from afar that the heat is running) and 4) any guess as to why my boiler won't fire from time to time?

Comments

  • Jon_blaney
    Jon_blaney Member Posts: 275
    How do you get the boiler to fire when you have the problem?
  • nickr
    nickr Member Posts: 22
    edited April 12

    How do you get the boiler to fire when you have the problem?

    I wish I knew. In the past I'd fiddle with a bunch of things until it eventually restarted, but there was no rhyme or reason to it. Now it's going longer between firing -- last time it fired it had been cold for 2 days, then randomly turned on in the middle of the night. It was on when we went to bed last night, and cold when we woke up. I haven't been able to get it started again.
  • Jon_blaney
    Jon_blaney Member Posts: 275
    Do this: Take the two wires off the thermostat and connect them together. Does the boiler start? If no, take the two wire off their boiler connection and replace with a jumper wire. Does the boiler start? Report what happens.
    Shalldierks
  • mattmia2
    mattmia2 Member Posts: 5,726
    does it have a vent damper?

    and don't let that tech touch your system.

    Was it not firing while the tech was there? It is really easy from someone even mildly competent to find that problem if it happens while they are there.
  • nickr
    nickr Member Posts: 22
    mattmia2 said:

    does it have a vent damper?

    and don't let that tech touch your system.

    Was it not firing while the tech was there? It is really easy from someone even mildly competent to find that problem if it happens while they are there.

    Yes it's got a 24v vent damper tied into the system. The usual sequence when the thermostat calls for heat is for the vent damper to open up and then the flames start roaring. But currently the vent damper isn't doing anything when the thermostat calls for heat.

    The boiler happened to fire up again the morning the tech came. So he said "it's working, so there's no way for me to know what the problem is."
  • nickr
    nickr Member Posts: 22

    Do this: Take the two wires off the thermostat and connect them together. Does the boiler start? If no, take the two wire off their boiler connection and replace with a jumper wire. Does the boiler start? Report what happens.

    I disconnected the red and white wires from the thermostat, touched them together, and the boiler fired up!!! Does this mean I just need a new thermostat? (And can I use the existing wiring as a c-wire?)
  • mattmia2
    mattmia2 Member Posts: 5,726
    Was it not working when you touched the wires together and it fired up? You have to try the jumpering stuff when it is not working.

    The vent damper has a switch that closes when the damper opens to interlock the burner and keep it from firing when the damper is closed. If either the damper sticks or the motor fails or the switch goes bad the burner doesn't fire. There is a whole chain of other safety devices and the thermostat in series with the burner but the vent damper is one of the most common ones to fail since it opens and closes every heating cycle. Has anyone been testing the low water cutout regularly?
  • nickr
    nickr Member Posts: 22
    mattmia2 said:

    Was it not working when you touched the wires together and it fired up? You have to try the jumpering stuff when it is not working.

    The vent damper has a switch that closes when the damper opens to interlock the burner and keep it from firing when the damper is closed. If either the damper sticks or the motor fails or the switch goes bad the burner doesn't fire. There is a whole chain of other safety devices and the thermostat in series with the burner but the vent damper is one of the most common ones to fail since it opens and closes every heating cycle. Has anyone been testing the low water cutout regularly?

    The boiler was cold (hadn't fired all day) when I touched the two wires together. It immediately fired up.

    I just moved in last year. My sense is that the system hasn't seen much testing or service in a while, LWCO included.
  • mattmia2
    mattmia2 Member Posts: 5,726
    Then that would tend to point to the thermostat. You should find someone that knows what they are doing to clean the boiler and test all the safeties.
  • Jon_blaney
    Jon_blaney Member Posts: 275
    I would replace the thermostat. Does the old one have batteries? Maybe that is all it is. There are Youtube videos on how to wire a thermostat if you have no c wire.
  • neilc
    neilc Member Posts: 1,805
    immediately fired up when the thermostat was jumped?
    or with the slight delay for the vent damper ?

    cause if it lit off immediately, you still have an issue with the vent damper,
    and if the damper is closed, you should not be lighting immediately
    known to beat dead horses
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,321
    edited April 13
    With the incorrect diagnosis and wiring suggestions I would ask for a refund. The technician clearly needs some schooling. I'm sure he believes what he said, but he was incorrect about the vents and the wiring.
    You might show him this picture and ask the question "What does C mean in this picture?"

    As far as the extra wires, you can certainly use one of them to connect the C terminal on the thermostat to the C terminal on the transformer. Just be sure the R on the thermostat is connected to the transformer. In some cases W on the old thermostat is connected to the transformer and it works. But when you need a C to operate the thermostat, then W on the thermostat to the transformer will not work. Be sure by looking at the boiler wiring diagram.

    CAUTION. if you are not familiar with control circuitry, you can damage some parts if you jumper the wrong terminals.As far as checking what is not connecting when there should be a call for heat, The Tech was correct. it could be any number of things like the Thermostat, LWCO, Pressuretrol, ... OR... the vent damper.

    With the covers off of the controls you can easily determine which one it is. Just use a jumper wire to see which one is open when it should be closed. like in the diagrams below

    When the problem presets itself, take a jumper wire across the R and W on the thermostat, if the burner starts or the vent damper starts, then that is the problem control. If not...

    Move on the the next control in line and jumper the contacts that are open for an unsafe condition, and closed for normal operation.

    Continue down the line until you find the problem devise.

    Once you have located the open circuit, then you must determine if it is open because it is supposed to be, or if it is malfunctioning. then take appropriate action to correct the problem.


    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • pedmec
    pedmec Member Posts: 198
    when working on heating systems we always say safety first. DON'T LET THAT TECH BACK IN YOUR HOUSE
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,321
    If my diagram above is not exactly like your system, you can post the model number and brand, or take a pic of the wiring diagram and I can make you a personalized diagram and point out where you can check the different devices.

    CAUTION. if you are not familiar with control circuitry, you can damage some parts if you jumper the wrong terminals.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • nickr
    nickr Member Posts: 22
    neilc said:

    immediately fired up when the thermostat was jumped?
    or with the slight delay for the vent damper ?

    cause if it lit off immediately, you still have an issue with the vent damper,
    and if the damper is closed, you should not be lighting immediately

    The proper sequence (vent damper, then fire) activated when I touched the red and white wires.
  • nickr
    nickr Member Posts: 22


    As far as the extra wires, you can certainly use one of them to connect the C terminal on the thermostat to the C terminal on the transformer. Just be sure the R on the thermostat is connected to the transformer. In some cases W on the old thermostat is connected to the transformer and it works. But when you need a C to operate the thermostat, then W on the thermostat to the transformer will not work. Be sure by looking at the boiler wiring diagram.

    CAUTION. if you are not familiar with control circuitry, you can damage some parts if you jumper the wrong terminals.

    Very very informative. But I'm gonna respect my limits here and have a reputable tech come in and a) verify that it's the thermostat that's malfunctioning, and b) hook up the common wire for the new thermostat.

    Any recommendations on a solid "smart" thermostat with cph settings?
  • nickr
    nickr Member Posts: 22
    edited April 13

    If my diagram above is not exactly like your system, you can post the model number and brand, or take a pic of the wiring diagram and I can make you a personalized diagram and point out where you can check the different devices.

    I drew the wiring connecting the thermostat, transformer, and boiler:



    Here's the boiler. It's a Utica PEG150CDE.






  • nickr
    nickr Member Posts: 22
    Wiring

  • nickr
    nickr Member Posts: 22
    edited April 13

    Here's the drawing of the wiring between thermostat/boiler/transformer.
  • mattmia2
    mattmia2 Member Posts: 5,726
    Where does that wire from the ceiling go after it disappears in to the ceiling?

    Where does the cable from the thermostat go?
  • nickr
    nickr Member Posts: 22
    edited April 13
    mattmia2 said:

    Where does that wire from the ceiling go after it disappears in to the ceiling?

    Where does the cable from the thermostat go?

    Hopefully my drawing clears up those questions. Blue and green wires from the transformer route down to the boiler. Thermostat's wires go to the boiler, but only the red and white. The others just terminate unused. I want to use one of those as the common wire.

  • Jamie Hall
    Jamie Hall Member Posts: 19,137
    Do yourself a big favour. (Besides keeping that tech. out of the house, I mean...).

    Go down to your local big box store. Buy the cheapest two wire thermostat you can. In my local one it would be this one: https://www.homedepot.com/p/Honeywell-Home-Round-Non-Programmable-Thermostat-with-1H-Single-Stage-Heating-CT87K/100476730

    Take it home. Read the instruction carefully and hook it up as it says to. See if it activates the heating system as you want it to.

    If so, you've solved your problem. If you seriously want programming, there are two wire battery powered thermostats which do that, too.

    If you want fancy stuff like wi-fi or that sort of thing, you'll need that third wire -- but try it with the easy stuff first.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,321

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • nickr
    nickr Member Posts: 22


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,321
    edited April 13

    I can offer you a wiring diagram for a wifi thermostat (most brands) that require a C terminal to operate using an isolation relay and a separate transformer. But I would check out the problem using @Jamie Hall's idea using a cheep thermostat to see if that solves your problem first.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,321
    edited April 13
    Based on your diagram, my simplified diagram looks like this for your system.

    Since the R from the transformer (in your diagram the Brown Wire) is not connected to the thermostat directly, if the LWCO or the Pressure control ever opens (as it should from time to time) the thermostat will consider that condition as an error. So normal cycling of the Pressure control or the LWCO will cause a thermostat failure.

    I hope this helps with your understanding of the wiring requirements.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • Chris_L
    Chris_L Member Posts: 258


    If you want fancy stuff like wi-fi or that sort of thing, you'll need that third wire -- but try it with the easy stuff first.

    If you don't have a C-wire and don't want to install one, there is another way to have a wifi thermostat.

    You can get a battery operated thermostat that communicates wirelessly with a hub that is connected to the internet (and requires an outlet). Google Zigbee thermostat and you'll find a bunch.
  • STvex
    STvex Member Posts: 48
    The original Nest Learning and Nest E thermostats don't need a c wire.  My old steam boiler had a nest e thermostat.  The new nest thermostats need a c wire.