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.

Thermostat calling for heat; boiler does not come on

<span style="font-size:12pt">Our heater has been running a lot this winter and without problems for the most part. On maybe ten occasions, though, the thermostat is calling for heat and the pilot light is on, but the boiler did not come on. On a couple of occasions, the boiler came on by itself some time later. On other occasions, I loosened the screws for the wires on the pressuretrol (see close-up; one comes from the thermostat, the other goes to the low-water cutoff), jiggled them, and the boiler came on. Not tonight, though …</span>

<span style="font-size:12pt">Information on our setup:

One-pipe steam heat

Millivolt system

Cut-in pressure: 0.5 psi

Differential is set to 1 for a cut-out pressure of 1.5 psi</span>

<span style="font-size:12pt">What we tried (other than jiggling the wires):

Made sure that water level is fine

Checked for blockage at the base of the pressuretrol where it connects to the pigtail

Cleaned the pigtail

Checked/cleaned low-water cutoff

Rapped the pressuretrol with the handle of s screwdriver

Replaced the millivolt wiring at the boiler</span>

<span style="font-size:12pt">Does this sound like a new pressuretrol would help? It is my understanding that they rarely go bad, but is there anything else worth trying that I am overlooking? Thanks much for any feedback!</span>


  • BobC
    BobC Member Posts: 5,479
    edited February 2014
    Try this

    Try pushing down on the box beam just below the pressure scale where I marked it, if the boiler comes on it means the pressuretrol is faulty. By pressing that beam down you should cause the switch to make.

    ERROR - don't push down, try prying it up to force the pressure plunger down a bit

    You could try taking the pressuretrol off the pigtail and make sure the base of the pressuretrol is clear and also make sure the pigtail is clear as well.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Paul48
    Paul48 Member Posts: 4,469

    Closer....that's  .1 and .5
  • Martinle
    Martinle Member Posts: 3
    Thanks and update

    Thank you for your quick replies.

    I pushed down on the beam, but the boiler did not come on. Base of pressuretrol and pigtail are clean.
  • Paul48
    Paul48 Member Posts: 4,469

    Push down?
  • Martinle
    Martinle Member Posts: 3
    Saw the correction

    I now pried it up. It's still not working, though. :(
  • Jamie Hall
    Jamie Hall Member Posts: 23,449
    Using a good

    ohmeter, turn the power off, disconnect the wires to the pressuretrol, and measure the resistance between the terminals.  If the contacts are good in the switch, and the switch is closed, you should read 0.0 ohms.  Maybe 0.1.  Anything more than that, bad contacts in the switch.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nicholas bonham-carter
    Using a jumper wire

    If you have a wire with alligator clips on the ends, then you can jump out the safeties one by one in order to find the inoperative one.--NBC
  • Fred
    Fred Member Posts: 8,542
    What about the LWCO?

    Do you manually feed water to this boiler? If it doesn't have an auto feed, the Low Water Cut Off switch could be stuck open. If you have an auto water feed, it is probably not the LWCO or it would be flooding the boiler. If you find it is not the Pressuretrol or the LWCO and you are sure your thermostat is functioning (should hear a click at the boiler when you turn the thermostat down (below current room temp) and then back up (above room temp), then it is probably the gas valve stuck closed. One other thought, is their a damper on the flue? If that is stuck closed, the boiler would not kick on either. Several things to look at.