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Boiler Does Not (Always) Come on

<span style="font-size:12pt">We have one-pipe steam heat in our 1926 house and absolutely love it. About a week ago, temperatures in our area dropped enough that we needed heat at night, and for the most part, it’s been running just fine. On a couple of days, though, the boiler did not come on when it should have based on the thermostat setting. T-stat is working fine and the pilot light is on. On one occasion, I didn't do anything and an hour or so later, the boiler came on. Not this morning, though … :( What are the most likely reasons for our issue? Thanks in advance!</span>


  • JStar
    JStar Member Posts: 2,752
    edited October 2012

    Could be any one of the controls or safeties. Anything would be a guess.

    Where are you located? Maybe somebody local can help.
  • A couple of things

    a plugged up pressuretrol or a plugged up water feeder could be the culprit
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert

    Noisy Radiators are a Cry for Help
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    boiler not coming on

    if you have a slow return, the boiler may have been temporarily starved of water (for that hour). can you observe whether the waterline is dropping while firing?--nbc
  • vaporvac
    vaporvac Member Posts: 1,520
    Gas regulator?

    I am NOT a professional, but had something similar happen last year when the diaphragm on my gas regulator died.  If your boiler is very old or still has the old components with new sections this my be the case.  Obiously the pros here know best, and advised me well.  it wasn't obvious as it was intermittent and totally random.  Sometimes it would be hours and then, voila...heat! However, it was a downward trend and needed replacing. Good luck.  CTD
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    intermittent boiler

    to find out where the problem lies, the wires to the thermostat will have to be jumped to simulate a call for heat. a number of repetitions may be necessary to duplicate the failed start. then the safety switches for pressure, and water level, should be jumped together. if the boiler starts, then the safeties can be disconnected in sequence to find out which one is causing the problem.

    the connections to the jumpers should be made with care as some controls carry low 24 volts, while others may carry 110 volts. 

    you may find that the low water cutoff is the culprit, with a sticking float, or dirty probe. when was the last time the boiler was serviced?--nbc
  • BobC
    BobC Member Posts: 5,477
    Another possibility

    As mentioned it could be a slow return or it could be the pressure detecting safety. A steam system has a pressure limit to shut the boiler down when the pressure reaches a predetermined limit (usually 1-1/2 to 2PSI). Pressuretrols with microswitches in them sometimes get flaky with age.

    If you catch it when it's not working try a couple of things. first does the water level in the gauge glass look normal? if it's low you could well have a partial blockage in the wet return that is feeding water back to the boiler to slowly. In that case the wet return will have to be cleaned out.

    Second try rapping the pressuretrol with the handle of a screwdriver to see if it actuates, if it does start to work it's time for a new pressuretrol. Also as stated before it could be crud in the pigtail or the base of the pressuretrol, the pigtail should be removed and checked to make sure it's clean.

    Post some pictures of the boiler and the piping around it so we can see what your dealing with. Show the pressuretrol (or vaporstat) and give us a shot of the boiler return piping also.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Martin Gritsch
    Martin Gritsch Member Posts: 5
    Thank You!

    Thank you very much for all the advice. Shortly after I wrote the post, the boiler came on and has been running without problems since then. I am assuming that it realized that resistance was futile since it was up against the cumulative knowledge of “The Wall.” :) Thanks again to all of you for so generously sharing your expertise.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Intermittent problems

    I hope the next time the boiler refuses to start, it is not -20 degrees!

    It would be so useful if the safety device manufacturers would incorporate some led status lights into their products. Then you could have gone downstairs and seen from the lights what part of the control system was at fault. As it is, you now have no knowledge of whether this is a serious issue or not.

    Maybe some bright spark (with or without an oscilloscope ) can devise an add-on status panel to show the non technical homeowner what to tell the tech over the phone.--NBC
  • BobC
    BobC Member Posts: 5,477

    That might cost them a nickle, and all those nickles help pay for the marble privy that comforts the poor misunderstood CEO.

    I was sentenced to work for the post office as a mail processing equipment technician for the last 8 years of my working life after the engineering job went across the pond. All of the equipment had emergency stop circuits that ran on 24vdc and had 3 poles that would interrupt the machine control power, signal the maintenance bus, and light a bulb on the switch itself.

    Processing mail creates a lot of paper dust and that dust gets into everything, especially cheaply made switches that were designed to interrupt motors. I contacted the switch maker and asked if the switch was rated for use on a dry circuit (low voltage and current) and there response was the switch was rated at 10a 240v. So what we had was a 130 ft long machine with 40ea 3 pole intermittent switches and no easy way to get at the connections without tearing things apart. I learned the quickest way to identify the balky switch was to strike each switch with my folded multitool and that would cause the contacts to jump and uncover the bad contact.

    They thought they were being clever by having multiple poles on that switch but all they did was multiply the problems we saw.

    The road to hell is lined with good intentions

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
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