I recently replaced my Rheem RTE13kw tankless water heater with the newer version of the same heater(RTEX13KW). The new water heater causes a group of wall lights that are all on the same switch to dim...no other lights in the house are affected. While the water heater is running the internet will not work at all, and the radio will have a lot of static. The old water heater never had these issues. The lights dim the worst when the water is on low and when only the #1 heating element is on. With the water on high the lights seem fine, but the internet still doesn't work. I have run all the diagnostics on the heater that Rheem provides in the troubleshooting guide and I have found no issues with the water heater. If there is anybody that can give me some ideas it would be very helpful.

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    Get a multimeter. Check voltage on 120V (both sides/poles/legs, if you can figure out what's what) and 240V circuits when the heater is off, running "water is on low" and any other modes. That way we can see if this is a "simple" voltage drop or if there is possibly something more serious (e.g., a neutral problem) going on. Mar 8, 2020 at 4:25
  • @manassehkatz-Moving2Codidact -- I doubt it's anything load-related because the old water heater was also a tankless, apparently of the same rating? Mar 8, 2020 at 4:48
  • @ThreePhaseEel You may be right. But sometimes things get a bit "confused" during installation. Easy enough to check. Mar 8, 2020 at 4:51
  • I did check the voltage coming in, together they were 242V...I did not check them individually. The voltage on the heating elements when the water was running is 237V on both of them. Both heating elements had 9.7 ohms, the speck is between 6 and 10 ohms. I am not sure what you mean by a neutral problem...there are only two wires(120V each) and a bare ground going into the heater. That wire was factory installed and came with the heator. I wired that wire directly to my breaker box with a 2 poll 60A breaker. I know it should have its own box but that is how the original water heater was wired Mar 8, 2020 at 5:05
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    It's a wire connection problem. Weeza need some photos. Mar 8, 2020 at 5:12


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