FYI...had electrical problems with a Vena AC/DC monitor once, every time the Water heater would start the meter would go crazy for a while. I checked and found the ignition lead for the Water Heater resting on the DC wires. So the ignition spark was sending interference through my DC system. After I moved the ignition wire a few inches away from the normal DC wires, I never had a problem again.
might be worth checking.
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