We have an Whirlpool 50 gal 240v water heater (4500watt elements) that was installed by a plumbing company in 2016. We had zero problems with it until last week when it started tripping the breaker.
After flushing and inspecting the tank (it looks good) I replaced both heating elements and thermostats.
The breaker still continued to trip.
I tested the wire for continuity and visually inspected what I could reach including in the attic, it seems fine. But the breaker for the water heater is only 15amps, which I thought seemed low for a water heater this size. So, not wanting to change anything I replaced the breaker with an identical new 15amp breaker.
The breaker still continued to trip. Not random, not immediately, but after the heater had been operating to reheat water, like after a shower.
Some online research leads me to think the correct breaker should be 25amps (stated in manf install guide for 240v 4500w). So for a test I swapped the 15amp breaker with a 20amp I had on hand (this is in a 100amp sub panel that can support this increase) and ran a temporary 10ga wire (in wall wire is 12ga) to the heater.
The breaker has not tripped since. It does not get warm, nor does the wire. The water heater is working fine.
After investigating all possibilities it seems the most likely issue is an undersized breaker. So my question is:
Is there another possibility at this point?
Could it be we were somehow skating by all this time on an undersized breaker?
Is it possible the old elements somehow stayed under 15amp but then failed causing the breaker issue and the new elements pulled just enough more to continue tripping the undersized breaker?