I recently installed a Rheem Retex-18 tankless electric water heater. When I turn the heater on I experience many electrical issues around the house:

  1. Sense home energy monitor freaks out and turns off
  2. Smart thermostat exhibits a loud buzzing
  3. Breaker panel buzzes loudly.

More information:

The cable run is about 40 ft, and uses two 8AWG cables and 2 40A dual pole breakers. The heater operates normally, and I even notice that there is very little flickering from lights when the heater is on. I measure a <2VAC drop when the heater is under load. The breakers do not get hot. I checked the ground connection and it appears to be fine. The house has a 200A service, and I live in an area where most houses have electric baseboard heating, so I expect that the service is sized appropriately. Walking the street it seems like every pole pig is serving 3 -4 houses. I tested this both when the temperature outside is hot, and when it is cold, so my local load does not seem to be an issue. I checked to make sure that the cables are not reversed on the heater and they are not. Both elements are receiving each phase in the same order. I tried turning everything in my house off, and just turning the heater on and still experienced the same issue, even with a flow rate low enough to only pull 10 KW. The connections to the breaker, and the breaker to the panel seem to be sound. Panel type is a Eaton CH.

Any idea what is causing this?

  • Do you know what your total load is for the house? Since your water heater is 240v and you are not having an issue with maintaining voltage it sounds like your connections are good. Is your meter directly behind your panel? I had a meter issue 1 time when adding a big load caused by the meter. The power company brought out a new meter and it fixed the problems I was having a high pitch noise but it was from the meter on the other side of the wall.
    – Ed Beal
    Commented Apr 8, 2020 at 22:40
  • A complement. You are a "new contributor" yet did a GREAT job in providing needed information to answer your question. You diagnosed many potential issues, presented that and asked a specific question. Welcome to SE. Commented Apr 9, 2020 at 1:02
  • Thanks @GeorgeAnderson! Ed- My meter is directly behind my panel. I have not heard any noises up and to this point, but I will listen more closely tomorrow.
    – Rnance
    Commented Apr 9, 2020 at 3:28
  • It's an installation issue. We'll need detail/photos of how the wiring was routed. Commented Apr 9, 2020 at 15:27

1 Answer 1


From the Rheem website for this model:

"Most advanced self-modulation, adjust power to meet hot water demand."

Most likely, that means it is using an SCR based controller (solid state power controller) to do variable power control of the heater elements and the phase-angle firing of the SCRs is causing extreme line noise and harmonics that is affecting other devices when it is on. Not a lot you can do about it, but in small doses as a HW heater would run, it's not particularly harmful. If it is causing severe negative effects that you can't stand, you could try having someone install a Line Reactor or an Isolation Transformer ahead of the HW heater. That will not be inexpensive though.

  • Thanks for the info. I took the cover to the unit off, and there are two large components (3 legged in a package that looks like the big, big, big brother to a TO-220) that I suspected are Triacs. My surprise was the amount of noise being put on the line. I hooked a scope up (unfortunately all I have access to right now is a current probe) and monitored the line going to the sense power meter. There was a ton of garbage on the line. This cannot be happening in all installs. If so I cant imagine that it would pass FCC tests.
    – Rnance
    Commented Apr 9, 2020 at 3:23
  • 1
    I am skeptical. Line noise doesn't make panels vibrate. But eddy currents do! Commented Apr 9, 2020 at 15:28

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