Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Thermaflow biler with Honeywell R2784 control and Beckett 21805 burner

8-year old Thermaflow boiler, Honeywell R2784 controller and Beckett 21805 burner. Ongoing problems the last 7 years. Boiler has shut down over 40 times. Each time I get a "hard lockout" message on the controller. Three different and reputable boiler companies have tried 9 times but can't fix it. New Roth upright oil tank installed and new oil lines. Boiler control has been replaced twice and the burner has been replaced once. Can anyone help?


  • HVACNUTHVACNUT Posts: 2,172Member
    Did the problem start after the Roth tank? 2 pipe oil lines?
    The truth is, there's so much to check, but not so much that a qualified tech couldn't figure out.
    The start would be smoke and combustion tests.
    The burner is a Beckett AFG by the way. 21805 is the motor.

    What model Thermoflo?
    If they replaced the whole burner, (unbelievable) was the new one set to OEM specs? Then start the test and adjust.

    Has a vacuum test been done on the oil lines?

    Did anyone check cad cell resistance or the ignitor?

    It's a little ridiculous you've had to deal with this mess for so long.
  • STEVEusaPASTEVEusaPA Posts: 2,903Member
    I agree with @HVACNUT Nuisance lockouts can be tricky sometimes, but 40 times is way too much.
    Every component can be checked with proper tools and more importantly skills.
    Did anyone scroll thru the history on the controller for any clues?
    At minimum I would put a ProMaxx on there for some diagnostics.
    If I were really stumped, I'd put my OnWatch data logger on to it and let it log everything until it locked out.
    I'm really leaning toward a vacuum leak, improper bleed, I'd test that first, along with checking the ignitor, motor pump, pump cut-off. Could even be a slipping coupling.

    BTW, I'd first check incoming power to make sure it's clean, and check with you about any huge electric usage.

    ~~another boring story~~
    Years ago (20?) when my Dad was doing service, 3 nights in a row around 10pm was getting a call about a furnace locking out. Well they noticed it was cold in the house about 10pm.
    Checked everything, couldn't figure it out. Older house, fuses, limited, undersized electric service
    The next night, no heat, I went with him. First thing I noticed was a drum set and some electric guitars, and keyboards.
    So I asked if the 'band' had been practicing the last 4 nights...'Yea'. They just started using this basement for practice the last 4 days, and stop around 9:30.
    Although no fuses popped, I assumed the huge current draw must have been something the primary control didn't like (grounding/neutral?).
    I told them either turn the heater off during practice, or get an electrician out here to figure out how to power this equipment properly, or stop practicing down here.
    Never got another call back for the rest of the time they were a customer.
  • GBartGBart Posts: 753Member
    Could be anything, new roth tank, let me guess, 2 line system pumping 20gph though a 13 gph filter, after 2 months there's enough restriction in the filter to slay the pump and out the fire goes
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!