Loud horn noise on Lochinvar Cadet the day after inducer motor replacement

dhw_probs

I just had a tech in yesterday to replace the inducer motor on my Lochinvar Cadet 120k BTU.

Since then, I've had a new problem: As often as about every 10 minutes it will give off a loud horn noise like a semi truck, lasts for about 5 seconds. Sometimes it will go hours without doing it, then do it often.

It seemed like it was doing it when firing up, and I was able to fairly reliably reproduce it by hitting the reset button and waiting for it to come back up. I was watching through the little glass hole where I can see the flame, and the noise happens about 1 second after the flame ignites.

Steve Minnich

Did the tech check gas pressure and do a combustion analysis after the repair?

HVACNUT

Is this natural or LP gas? I recently had a call for a horn noise where the installer didn't install the LP orifice. This wasn't a Lochinvar but its something to check. The tech had to remove the gas valve to replace the blower and the orifice is right there.

dhw_probs

Thanks to both replies... Sounds like it's nothing user-serviceable, so I'll have to get them back.

Ironman

Is the any CSST in the gas line? If so, that’s the SOURCE of it. Having the burner not properly tuned to the richer side of the manufacturer’s specs can cause the resonance when CSST is used.

If proper tuning doesn’t alleviate the problem, then removing the CSST, or using a larger diameter should.