Peerless MI Gas Boiler, Pilot is On, won't fire

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  • Peerless MI Gas Boiler, Pilot is On, won't fire

    Peerless Gas MI Boiler 13 years old. LWCO switch and pressure relief replaced a couple of weeks ago, been working fine since.

    Woke up this morning to a cold house. Boiler was cold, pilot light was lit. Checked vent spill switch, it was not tripped. Blipped the aquastat relay, the damper opens, makes all the noises but won't fire (damper shuts). Tried a couple more times then gave up. I walked away, came back and it had fired up all by itself. I looked for an igniter in the manual but doesn't seem to have one. I changed the thermocouple last year and cleaned that valve. My question is, how does the boiler fire up, if there's no igniter? What else could be the problem?

    I am looking into replacing the gas valve. It can be ordered on Amazon. I also ordered a flame roll-out switch. Have not tested that - but would that cause intermittent failure?
    Last edited by joeysmith2021; 01-08-2021, 03:47 PM.

  • #2
    The boiler ignites from the pilot light. If everything is right, the gas valve opens and that's it.
    You may be on the right track with replacing the gas valve.
    test the wires at the gas valve to see if you have 24 volts, if you do and the pilot is lit, there is a good chance the gas valve is not opening.

    If the rollout switch burned out the boiler would not fire at all. it is not an intermittent part once it burns out it needs to be replaced.
    I answer all plumbing and heating questions, all day long.

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    • #3
      The wires wil have 24 volts when the system tries to fire right? I noticed that the damper closed and got quiet when it did not ignite. Just want to make sure when to test it.

      Thanks!

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      • #4
        Okay is the pilot lit all the time? or does it lite when the damper opens?
        I answer all plumbing and heating questions, all day long.

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        • #5
          I have the version where there's a pilot light all the time. In the manual it shows two versions, one with an always-on pilot light and another with an electronic igniter. The damper opened when I blipped the relay in the limit box, the sounds of valves opening started, then it all shut down when it couldn't fire up. That kinda tells me the limit box sends the 24v when the system is firing up. Since it's working, I can't test for the problem situation. It's been working all day, but I ordered the gas valve just in case. I can always return it if it turns out to be something else.

          I should mention one thing, when the plumber put in the low water cutoff, he splashed water all over the limit box sitting below it as apparently there was some water left in the system. It had the cover on so I don't think it got all wet. Didn't seem to harm the unit. It's been controlling everything pretty well for two weeks. That's the other expensive part that I might have to replace right? The plumber said he'd pay for it if it was busted because it was his fault. He also said these Peerless boilers had these little niggly problems all the time.














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          • #6
            How many thermostats do you have? for now, I'm thinking it has nothing to do with the gas valve. If the house is calling for heat and the boiler is cold, the damper should stay open and the circulator should keep running even if the gas valve does not open. are you sure the boiler is cold?
            what does the temperature gauge read?
            I answer all plumbing and heating questions, all day long.

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            • #7
              Gauge was at zero this morning, boiler was stone cold. Damper was shut until I blipped the relay on the limit box. Then it turned off again when the furnace did not fire. I have two zones and both thermostats were asking for heat this morning. The thermostats are Emerson Sensi wifi's wired with common ground. Batteries are fresh and show as much on the digital display. Displays said room temps were 62 with temp setting at 68. Right now the furnace turns on and off when I raise or lower the temps on the thermostats. What are the chances that both thermostats are malfunctioning at the same time?

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              • #8
                The chances of both thermostats failing at the same time are very low, but anything is possible. In my experience, the thermostat is almost never the cause of the problem.
                I think the problem is with an end switch or an end switch wire being loose. the end switch makes contact with the boiler control ( T T ) terminal when a zone valve opens all the way or a zone control gets a signal from the thermostat. This makes the boiler fire.
                It could be a control problem too.
                I answer all plumbing and heating questions, all day long.

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                • #9
                  I think the "brains" of the system is that "limit box" that sends the 24v to the damper and the fuel valve, etc. That would be the potential source of the control problem right? If it happens again I will test for voltage.

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                  • #10
                    Yes, it is the brains of the system, but if it does not get a signal to come on, the problem is with something before the control.
                    Next time it fails, jump the T T terminals in the control to see if it fires. if it fires the problem is before the control.
                    I answer all plumbing and heating questions, all day long.

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                    • #11
                      Thanks much, if it happens again I have a much better course of action.

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                      • #12
                        It has not recurred in more than a week. In the meantime, I have received the gas valve that I ordered. Should I send it back or install it as a matter of course? The system is 13-14 years old and I don't know how long these things last.

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                        • #13
                          Just keep it in a clean dry place until you need it.
                          I answer all plumbing and heating questions, all day long.

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                          • #14
                            Ok I caught it just now. The thermostats were both asking for heat and the furnace was stone cold again. I tested the leads at the gas valve and it said 0 volts. I pressed the reset button on the lwco because that usually starts a few things like the damper - the damper opened but no change. I tapped the limit box (just the enclosure and not the solenoid) and suddenly it got 24 volts! I hooked it up again and it didn't fire until I tapped the limit box again. It fired and is on now. I will check for any loose connections in the limit box but based on this test can I assume it's going bad if I don't find anything?
                            Last edited by joeysmith2021; 01-19-2021, 10:11 PM.

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                            • #15
                              No, you should not assume it is the control box yet. The next time it happens don't tap anything, jump the TT terminals. If it starts the problem is in the end switch wires before the control, if not it is in the control or after the control. The tapping could have caused a loose wire to make contact, in the control or before the control, or after the control.
                              I answer all plumbing and heating questions, all day long.

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                              • #16
                                My bad, I didn't jump the TT because I felt the TT Control valves going. Next time I'll take the TT off the wall and jump the wires. While inspecting the control box, I tightened power screws checked wires, also found the terminals on the control box that leads to the gas valve -- should be 24 volts there but upstream is the damper. Also upstream is the LWCO, I remember the plumber had a bad connection there which prevented the system from firing - I will check that now.

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                                • #17
                                  We may be having a misunderstanding, When I say T T terminals I am talking about 2 terminals in the control box.
                                  You said you would take the T T off the wall?
                                  If you can please post a picture of the inside of the control box, so I can see what you have and point out what I am talking about.
                                  I answer all plumbing and heating questions, all day long.

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                                  • #18
                                    I assumed you meant the thermostat lines that connect to the board at the top of the picture? I meant jumping the thermostat leads which would have the same effect?

                                    Attached Files

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                                    • #19
                                      It would have the same effect if there is no loose wire or other problem. So jumping it in the box will tell you if there is a problem between the thermostat wires and the control. jumping it at the thermostat will not tell you anything.
                                      I answer all plumbing and heating questions, all day long.

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                                      • #20
                                        Ok, I have a better shot at debugging this thing now that I know the places in the control box where I can check things. At least, now I know it wasn't the gas valve after all. First thing I will do when it happens again is to jump those terminals, then go from there.

                                        Note:
                                        After I tightened everything up, I did a simple test by jumping the TT terminals and it triggered the solenoid and the furnace fired up. I tried with the individual thermostats as well and the system fired up both times. The system is operational and there is no problem situation for me to check. I will have to wait until it happens again.
                                        Last edited by joeysmith2021; 01-20-2021, 03:14 PM.

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                                        • #21
                                          It's always hard to troubleshoot an intermittent problem.
                                          I answer all plumbing and heating questions, all day long.

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