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laars jvs minitherm pilot but no burner

I have a Laars Minitherm JVS.  I have a pilot but no burner when the t-stats call for heat.  It appears, the cut off circuit (flame roll-out , blocked vent , hi-limit) has continuity but I am not able to measure voltage anywhere.  In addition I jumpered the entire protective circuit and still no burner and no function of the automatic flue damper.  It appears the pumps are working and t-stat side is also functional.  I  


  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314
    time to call a pro

    jumping out the safety equipment is a bad idea even for a test. With the proper tools a decent pro will beable to get to the bottom of this for you and get the proper parts.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • TSV_Skibum
    TSV_Skibum Member Posts: 3
    noted, thank you

    noted, thank you
  • Plumdog_2
    Plumdog_2 Member Posts: 873
    Check the fuse

    Inside a  little black plastic holder (to the left of the transformer and relay) there is a fuse. If it blew, replace it with an identical one. The vent damper must operate before the firing cycle. You can manually open the damper (gently), and either place a switch in manual position or relocate a jumper wire inside the damper motor cover to provide temporary heat. Put the safety string back exactly as it was! That type of boiler can and WILL clog up and spill products of combustion (Carbon Monoxide). They have a recommended cleaning schedule.
  • TSV_Skibum
    TSV_Skibum Member Posts: 3
    edited April 2012
    checked fuse

    the fuse was good, I defeated the safety string while I was there with no intention of running for more than a few seconds to isolate the problem to the safety string. After the test all  safeties were returned to the  as designed configuration  

    Subsequent to this posting, I found the problem to be the hi-limit switch. The factory recommends its setting be 190 degrees, I found it to be set somewhat lower, about 140.  I reset the dial to the factory setting and the unit worked.  What bothers me is why the as found value was 140 in 1st place.  I am watching the operation closely, everything seems to be nominal.
This discussion has been closed.