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Strange Baxi Luna HT behavior

hot_rod Member Posts: 22,158
is it on the heat mode or the DHW mode? The one I have installed at my in-laws will short cycle when they have a low DHW flow, like a hand sink running.

It did have a loud hum whenI first installed it. I adjusted it out with the analyzer. It came back very low months later. Another fine adjustment on the gas valve handled it.

Short cycling in the heat mode could indicate a circ not running, or a very low heat demand.

hot rod
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream


  • Steve Goldstein
    Steve Goldstein Member Posts: 35
    Strange Baxi Luna HT behavior

    I had a Baxi Luna HT installed 1.5 years ago. About two weeks ago I noticed that it intermittently makes a strange humming noise. Sometimes the noise is steady (hmmmmmmmm), other times it pulses (hmmmm hmmmmm hmmmm).

    It's also doing a lot of short cycling (firing, then turning off, then re-firing), over and over again.

    It seems to exhibit these behaviors when the Baxi is trying to modulate down, not when it's at full fire, but I'm not certain of this.

    My HVAC contractor, who has been installing Baxis for two years, says he's never seen this behavior before, and is trying to get advice from the manufacturer (in Canada). In the meantime, I'm guessing some of you are familiar with the Baxi Luna (or the other brand/model that's just like it), and could offer some advice.

    Thanks in advance for your help,

  • Tony_23
    Tony_23 Member Posts: 1,033

    Have him check and set the low fire gas pressure. Also, make sure he runs a combustion analysis on it to spec.

    The short cycling is probably caused by input much higher than load. The minimum input is about 37K.

    Has he been only installing ? Has he been to the training meeting (not a sales dinner) ?
  • Roy_12
    Roy_12 Member Posts: 2
    moaning Baxi

    I'll go with Tony. It sounds as though you may have some flame instability on the burner. Check with a combustion analyser and see what the Co ppm is at.....on NG it should be no more than 50-55 ppm. If you have a higher reading you may want to check that your vent is still sound.
  • Steve Goldstein
    Steve Goldstein Member Posts: 35
    heat mode

    This behavior (the short cycling and the humming noise) are when it's in heat mode. The DHW side isn't connected.

    Is this unit damaging itself by short cycling?
  • Tim_41
    Tim_41 Member Posts: 153

    Did you try purging the HX again. Sometimes, debris can get in there and slow the flow down. Also, I once had the supply valve handle strip. The black handle. Even though the valve looked like it was open, it was actually closed.
  • Andy Byrnes
    Andy Byrnes Member Posts: 42

    How is it going with the magnets Roy?
  • Tony_23
    Tony_23 Member Posts: 1,033
    Hey Roy

    What happened, my good man ?

    No need to answer that here, just know I'll miss your insight and help.

    Tony Hilliard
This discussion has been closed.