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Old 03-14-2020, 05:21 AM   #1
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AquaHot circulation pump pulsing when Off - caused by Big Boy solenoid

I wanted to share this with the forum in case anyone else has this issue.

I have the AquaHot AHE100-04S unit. While walking around the Coach one day I heard a faint "motor pulsing" noise. I tracked it down to the #2 Circulating pump on the AquaHot. The AquaHot was not in use.

The #2 pump makes a pulsing noise (doesn't actually rotate more than a degree) and I can see the pump vanes turn back and forth slightly. Somehow there is a power getting to the pump when the unit is off. The LED light for Pump 2 on the control board also shows a dim flash/blink that matches the pulsing motor.

On the RV Hyrdronic Heater Repair forum, this same issue was posted. The poster "geneo57" figured out what is going on and came up with a fix.
RV Hydronic Heater Forum

The cause is that the Big Boy battery isolation solenoid is sending a DC pulse (it uses a low volatage pulse to keep the solenoid engaged) through the electrical system and that pulse is causing the AquaHot pump to pulse. I don't know if there is a problem with the Big Boy (works fine as far as I can tell) or if the problem is with the AquaHot (overly sensitive control board or failed capacitor on the board, or nothing wrong with AH).

The fix is to add a Capacitor across the Pos. and Neg. terminals that feed the control board. That filters out the stray pulse from Big Boy and stops the pump from pulsing.

The Capacitor is a 2200uF 35V

Just wanted to share this.
P.S. perhaps this Big Boy generated "pulse" is causing other problems with other electronic systems on the coach. But I have not noticed anything else acting strange. i considered adding the cap across the Big Boy terminals to remove the noise at the source, but in the end just did the fix as Geneo57 described it.
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Old 03-14-2020, 10:14 AM   #2
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Or a diode on the BIRD is bad?
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