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Intermittent Heat

QuincyQuincy Member Posts: 5
My home has a 4 zone hot water baseboard heating system that works well most of the time. However, roughly once each night the boiler will fail to fire even though one or more zone valves are open and calling for heat. The boiler will eventually cool to ambient temperature. When I manually reset each valve, the system has never failed to fire up properly. More system details are listed below. Any idea what may be causing this intermittent problem?

The single circulator works well. Each zone is controlled by its own White-Rodgers valve. The valves are powered by a large stand-alone transformer. The system is controlled by an L8148E aquastat. Its transformer powers the relay and the damper motor. I have never seen the damper fail to open nor the boiler to fire when resetting the system. I have checked out each zone valve and they appear to be working properly and sending the proper switching signals to the aquastat. I have checked out the boiler temperature sensor and it appears to be functioning properly. I also checked out the aquastat by jumpering various terminals to simulate the function of various switching signals. Everything appears to be working fine.

I suspect the aquastat relay may be having trouble making contact from time to time but I have never been able to observe it failing to contact.

My understanding is that if everything is working well the aquastat should fire the boiler anytime there is an active call for heat and the boiler temp drops 15 degrees from the high limit. Clearly, that is not happening.

I've consulted my local plumbing supply gurus but they are stumped.

Please help!!!

Thank you.


  • lchmblchmb Member Posts: 2,996

    you need to reset the system, is the damper in the open position or still closed? If open, you reset it, it then close's and reopens and fires? If so it could be the end switch in the damper itself. to test this, simply lock the damper in the open position. There should be a manual switch on the damper. If the problem persist's, replace your aquastat.
  • QuincyQuincy Member Posts: 5
    Intermittent Heat - Damper

    The damper is open when I find the system cold but with one or more of the valves open and calling for heat. When I manually reset the open valves, the damper cycles closed along with the valves. The damper opens again when the valves complete their cycle to open for a new call for heat. The gas valve also cycles and the boiler never fails to fire when I do this manual reset. Should the damper close whenever the boiler stops firing? Would make sense. If it isn't closing, would that prevent the boiler from firing up when the water temp drops 15 degrees below its upper limit? (I believe my aquastat is set for a 15 degree differential.) I had assumed that the boiler would fire up as long as the damper is open and that it does not need the damper to cycle closed and then open again when the boiler wants to fire.

    Having said all of the above I am not sure I understand the test you suggest. If I lock the damper in the open position that would seem to be reproducing what I already observe, right? From your previous comments I understood your meaning to be that the damper switch may be malfunctioning by indicating that the damper is closed (when, in fact, the damper is already open) and thus preventing the boiler from firing up and when the 15 degree differential is reached. If so, that would explain a lot because it appears to me that if the system is unable to heat the house enough to get the thermostats to stop calling for heat, and if the boiler won't fire when the 15 degree differential is reached because it thinks the damper is closed, then the system will continue to circulate water that is no longer being warmed. The thermostats would continue to call for heat and the water temp would eventually drop to ambient. Is this what you are suggesting?

    Sorry for the long explanation. Thanks so much for your time and help.
  • lchmblchmb Member Posts: 2,996
    no problem

    what generally happens, the zone valve opens and sends the signal to the boiler to cycle on. At that point the damper opens, once it reach's the full open position a switch close's completing the circut to the control and allowing the boiler to fire. Locking the damper in the open postion simply take's this out of the equation. If the problem is in the damper, your boiler will continue to fire without interuption. If the problem is in the aquastat your problem will continue and you will have ruled out the damper..
  • Paul48Paul48 Member Posts: 4,492

    I'd check the schematics for the damper. It may be physically open, but not making a switch to let the burner fire.The next time it happens you need to check everything that can hold the burner out.
  • furnacefigher15furnacefigher15 Member Posts: 514
    Flame failure

    If you have spark ignition, I would be looking at that as the trouble.

    If the ignition module goes into flame failure, the only way to reset if a gas fired unit, the only way to reset is to cycle the power off and back on.
  • Tim McElwainTim McElwain Member Posts: 4,436
    What is the make and number of the

    vent damper? It is very typical for the problem you are having to be caused by the damper either not opening fully of failing to close the end switches in the damper which then allow the rest of the system to function normally and fire. Send some pictures if you can to help us help you.

    Keep in mind in you over ride the damper function and the system then never fails your problem is the damper. This I realize was already suggested by others just repeating for emphasis.
  • QuincyQuincy Member Posts: 5
    edited January 2012
    Intermittent Heat - Damper Specs

    The flue damper model number is RVGP - KSF.  24 VAC. The datasheet is attached.  I have not yet tested the system with the damper held fixed in the open position.  Will do so soon and report the results.

    Thank you, everyone!
  • QuincyQuincy Member Posts: 5
    edited January 2012
    More on Flue Damper

    I set the flue damper switch to "Hold Open" (instead of "Automatic") while the damper was closed with no call for heat.  I expected the damper to open but nothing happened.  The weather has been quite bitter cold the past few days so I have not left the damper switch on "Hold Open" overnight.   The weather is expected to be a bit warmer the next few days.  I will see how the system responds with the damper switch fixed at "Hold Open".

    I've attached a photo of the flue damper.
  • lchmblchmb Member Posts: 2,996

    on the next call for heat the damper should open and cycle and after the end of the cycle the damper should remain in the open position....
  • QuincyQuincy Member Posts: 5
    edited January 2012
    Flue Damper

    So far, so good.  When set to "Hold Open" the flue damper did open on the next call for heat and as far as I can tell it has remained open and the calls for heat are being answered properly.  I will let it go for another 24-36 hours and see if the system continues to function properly.  If it does, I will assume that the problem I have is with the flue damper in "Automatic" mode, such as a contact not being made consistently.

    However, if the problem recurs with the damper in "Hold Open" I should assume the aquastat is malfunctioning.


    Thank you!
  • Tim McElwainTim McElwain Member Posts: 4,436
    edited January 2012
    Not necessarily

    it sounds like you have found your problem. Come back to us here if that is not the case and we will take you to the next step.

    By the way that is an Effikal damper which is now Field as they bought out Effikal.
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