Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Hydro Therm HI-125B with a LOW and/or Automatic firing?

This unit is from the late 80's according to tag and isnt very common or at least I can't find too much info on it. I think the controls have been updated but not sure. We purchased this house 2 years ago and inherited this boiler that has 4 zones and is our baseboard heat. It was operational for a few months after moving in and then summer of 2020 we didnt use it anymore. This house has a forced air system as a back up and works well so I wasnt too concerned about our boiler not firing up last winter. Fast foward to now and I would like to get the boiler fired up for this winter.

I am not a plumber although I play one at work, nor am I an HVAC/Furnace expert, but I have a multimeter and can use it. I am not familiar with all the terminology you guys toss around but I have a camera and and a solid sense of how boilers operate. I am most aware of the dangers involved and would rather not explain to my wife why we never woke up or why there is a pile of ash where our cabin used to be. So if this unit is scrap tell me and it's forced air for another winter.

I have repaired all the water leaks along the zone manifold with some new valves and will get a new thermostat or t-stat for this tomorrow. I will post some good photos tomorrow with better angles and sense of space. Is there a preferred T-stat I should be looking at or are they pretty universal for this application?

When I turn the power on I get 110v to all the correct locations and the transformer is sending 24v-27v to the relay(s) but without a thermostat I cant call for power. So I jumped the 2 wires that lead to the thermostat and get a loud "click" coming from one of the relays. Circulator pump does not show any signs of life nor the the (2 speed?) fan. I will look for any suggestions before going to the supply house tomorrow and post better photos. Thank you for any and all help , you guys are great communicating down to regular Joes.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    Why not just get a good tech in there to go over the whole thing for you-clean burners, check safeties, check gas pressure & combustion test.
    Then you know your starting from a good place.
  • CherryCreek1985
    CherryCreek1985 Member Posts: 4
    Thanks for the response Steve,

    That is a loaded question to my question, I have stayed married for 30+ years and it's partly because my wife does not call "the man" to fix anything. There are many more reasons I don't want to get a good tech to go thru it right now. Pride, Money, Location, etc, and Its not urgent. I want to make sure it can be saved and worth saving before I polish up any turds. I dont take my 2009 f-150 Platinum to the dealer for repairs either, I think I am trying to qualify or justify for an answer and I thought Heating Help was for people who need help.

    I forgot to mention this boiler burns Propane and the burners are new.
    HVACNUT Member Posts: 5,756
    edited October 2021
    @CherryCreek1985, Heating Help is definitely here to help but handing a loaded gun to someone with no firearms experience isn't help. Its something else entirely. 

    Even if you get the boiler running, how do you know its running safely?
    What's the gas pressure?
    What are the combustion numbers?

    Is there a wiring diagram anywhere? If you can follow that, using your meter, it will lead you to the fault(s).

    You'll almost always find with a system that old that it's not one particular thing, and everything must be checked and tested. You make the repairs on your truck, but do you do the state inspection yourself?

    I understand where you're coming from though. I gave myself a colonoscopy last week. You know, pride, money, and location. My wife fell in love with me all over again. 

  • CherryCreek1985
    CherryCreek1985 Member Posts: 4
    The old man who built the house said it is the original boiler and it has worked since day 1, this of course is after we purchased it so I figured he was shooting straight. The boiler worked our first winter and we had no issues so, I suspected its nothing major which is why I thought this site was a good place to start. I really only asked if there was a thermostat I should consider and kinda of an overview of what I had done thus far. I certainly was not asking for a loaded gun and now im stuck with a picture of you giving yourself a colonoscopy in my head.

    I'm sure you are very good at what you do and enjoy the daily banter with the people on this site, When I walk into a home, any home there are things that I look at and think **** are these people thinking and they really need to do this and do that. I had better make sure they get this old place up to code. There are safety measures even on a 30+ year old Boiler that would keep me from blowing the place up or shooting myself. Now I have spent more time typing and still no answers. In my business I deal with homeowners every day and live by a motto given to me by my first boss (my Dad). "Answer the question then give your qualifiers".
  • Jamie Hall
    Jamie Hall Member Posts: 22,947
    OK. First of all, @CherryCreek1985 , relax. As I am trying to do after reading your replies. You have basically told us "my truck doesn't start" and asked us "why". I have no doubt from your comments in your reply that if I told you my truck doesn't start and asked why -- even though it's a Chevy -- you could tell me exactly what to do to get it running. I couldn't, so let me answer the one simple question and then ask a few.

    On the thermostat, which appears to be your first question. Almost any inexpensive non-programmable thermostat should work. Keep in mind that a thermostat is only an on/off switch at heart, so if you take the two wires (for an older one) and short them together, the system should start. Simple.

    If it doesn't start, not so simple. You claim you hear a relay click. That's good. But -- what, exactly, does the relay do? Does it send 120 VAC to the circulating pump? Does it close a circuit to the gas valve? What does it do?

    What does send power to the circulating pump? That relay? Some other relay somewhere? An aquastat? If you energize the pump independently, does it run? You say you are getting 120 where it should be -- does "where it should be" include that pump?

    What sends power to that fan? Under what conditions?

    I can't make out what goes where in that junction box; you need to. In the absence of a circuit diagram, you really can't tell where either 120 VAC or 24 VAC is supposed to be -- or when. There are multiple safeties on that system; any one of them could be keeping it from firing.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    I already gave you the best answer, and @HVACNUT worded it better. Sometimes you have to call in some help. Sometimes the best help is to get some help.

    You don't ask the doctor how to perform a procedure because you like doing things yourself, right?

    The reason why I simply say to call in a competent tech is that as you are aware with something you are an expert in repairing, is you probably have a simple, straightforward way of diagnosing things, based on your experience and knowledge. In 10 minutes you can look and check a few things and quickly eliminate them to more efficiently diagnose the problem.

    The best, simplest advice I ever received about troubleshooting from my buddy, a really bright guy was this-"What is suppose to happen first? Then what is suppose to happen next?" And confirm with testing down the line until you find the failed component.

    So in your case, you closed T-T. You heard a relay close. First I would check your limits (safeties) is any one of them open. Then your pressure switch, then your gas valve and down the line.
  • CherryCreek1985
    CherryCreek1985 Member Posts: 4
    Thank you @HVACNUT, relaxation is what I do best and getting better at it every day. I appreciate your concerns and understand the complexities of this profession, I have called a reputable company and set up an appointment with a tech, unfortunatley as you know I wont know if he is a good tech until im commited. BTW I am picturing SGT. Hulka while reading your post and thats a backhanded compliment. @STEVEusaPA I'm getting my second colon probe mid November and will be thinking of you on that day. I find it odd/funny that you started this last post with "I already gave you the best answer" ...nope, you didnt answer the only question I asked. HVACNUT addressed my question on line five and gave a real scenario of events for the remainder of the post. It wasnt that it was worded better it was he answered the question. I am sure you are an expert on all things mechanical and your advice of getting a tech involved spot on, but to be the smartest guy in the room sometimes requires being dumb like a fox.

    Thank you
    Great Advice!!
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    Well the important thing is your not bitter.
    My first post I told you to get a competent tech. Your last post, you called a reputable company to get hopefully a competent tech.
    I don't know why you want to think of me while you're laying half sedated getting probed up your arse, but hey, whatever works for you.