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low co2 during combustion test

highwayhighway Member Posts: 7
Hello all. First post !! Did a tune up on a friends Thermo Dynamics series 110. Replaced the nozzle with same .85 80B. Pump pressure is 140.  I have an -02 draft over fire and -04 at the breach. I get a 9 to 10 co2 reading at the breach using a bacarach wet kit tester. I cant seem to get the reading any higher. I have the air almost completely shut. I'm I missing something? Thanks...


  • Paul Fredricks_3Paul Fredricks_3 Member Posts: 1,549
    More info

    Is it a Carlin burner in it? If so, what model Carlin. And 110 seems to be a common number for TD. Do you have the exact model number?
  • Big Ed_4Big Ed_4 Member Posts: 1,435
    Air Leaks

    Could also be air leaks dropping the % of CO2 ... Not a great boiler , reading would not alarm me as long a you have a 0 smoke ...
    I have enough experience to know , that I dont know it all
  • AudAud Member Posts: 1
    Draft over fire

    If it is a cwl or an ht, you may  have to much draft over the fire. The settings for Thermo-Dynamics' boilers our listed on the boiler.
  • highwayhighway Member Posts: 7
    low co2

    It has a beckett afg. The boiler calls for a -02 draft over fire, which I have. The chamber liner does have several cracks on the bottom or floor. I have 0 smoke.  Thanks for the replies.
  • billtwocasebilltwocase Member Posts: 2,385
    wet kit

    I would suspect that the fluid needs changing in you tester, as the readings aren't changing. I hope that you did another smoke test, and running a zero smoke. The only poor readings that I've gotten from these are high stack temps, which lowers the efficiency. They are probably the best steel boiler out there other than EK, JMHO. Try a digital tester on it, you may be surprised
  • highwayhighway Member Posts: 7
    edited September 2010
    low co2

    I have a new bacharach wet kit tester with approx 6 tests total. First I checked for smoke and got a zero reading. I then reduced the air and tested again for a trace of smoke. I then checked the co2 reading ( 9 1/2 to 10 ) and then increased the air and tested again for smoke getting a zero smoke reading. I thought it could be the tester, but I checked it on my own boiler when I got home and had a 12 to 13 co2 reading, so I assume the tester is working. My stack temp is 500 *
  • Robert O'BrienRobert O'Brien Member Posts: 3,222

    Leak between the base and HX,fairly common with drybase boilers
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  • billtwocasebilltwocase Member Posts: 2,385
    that or

    the flue collector is not sealed. Pull the burner and fully inspect the chamber, back and sides. Look for heat marks on the jacket midpoint
  • Robert O'BrienRobert O'Brien Member Posts: 3,222

    Bill is absolutely correct, i assumed that was checked when serviced
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