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Cad ohms

StingerIII Member Posts: 1
Burnham MPO 147, Beckett AFG, L1 Head, new primary R7284, new nozzle .85/60B, fuel pressure 150psi (strainer clean), Tiger Loop with new filter, flue pipe clear, boiler lightly sooted. Smoke pump missing from kit. Will check it later today and clean boiler.

Beckett OEM settings S7 / B1. At these settings Cad ohms are 1700
Closing the shutter to 3 brings it down to 1150.

Beckett says it should be 300 to 600 and to stay under 1600.

Any suggestions?



    HVACNUT Member Posts: 5,033
    edited November 2019
    You dont mention combustion analysis readings. At this stage its unlikely you'll get a 0 smoke. Draft readings? The air settings provided are just a guide for a starting point. You NEED the analyzer to properly tune the burner.
  • BDR529
    BDR529 Member Posts: 269
    HVACNUT is right. Flying blind without those readings. Also,Just get a delivery? How much bio? Seen delivery tickets indicate 10%-80%!! Bio-blends
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,133
    Same answer as I posted on the other site where you posted the same question...

    Could simple be your cad cell is dirty, or mis-aligned. Bad cad cell or bad cad cell wire. Your Z dimension could be off. Excessive heat could've hurt the cad cell eye, even though you have a 15 sec. post purge.
    First I would run burner, check draft/set draft, then do smoke test to get true zero smoke. Then take your CO2 number and open air shutter (not band) to drop that 1%.
    You can check the cad cell reading on the control, or put the wires on your meter and check them.
    Although the threshold is 1500 ohms on the older controls, like a 8184G, the newer Honeywells and Beckett Genysis won't lock out until 2500 or more ohms, especially with a head like an L1.

    I have an MPO 115 and never checked the ohms, just a combustion test. I wouldn't check ohms unless I had a problem.
    Draft is super important as that unit wants 0 at the port in the rear, and overfire positive. If you don't have the draft right you could be impinging on the target wall, creating soot and thus the higher (dirtier flame) ohm reading.