What size breaker needed for this water heater

Check size of breaker check cable load .

Check the name plate on the heater. You should see the amperage rating. For example, if it is rated at 30 amps, then you will need a 30 amp breaker. Do not use a larger rated breaker, that will defeat the purpose of it's safety use.

most water heater of that size is rated 240v, therefore it needs 2-pole. is it 240v rated? make sure you have a properly sized circuit breaker & matching conductors (wires) with the kw rating of the water heater

For residential water heater, 30 amp is best... but must have 10 gauge wire.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#trip-breaker
http://waterheatertimer.org/Color-codewire.html
If you have 12 gauge wire, then use 20 amp breaker and install 3800 watt elements in place of 4500 watt elements
http://waterheatertimer.org/How-to-replace-water-heater-element.html
Add a comment and say which size wire you have

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

State point-of-use electric water heater plugs in.
Check that outlet has power.

The water heater must be full of water or elements burn out instantly.
Test the element.
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/How-to-install-point-of-use-water-heater.html

Match voltage to water heater:
This electric water heater, like all electric water heaters, will work on 120Volt, 208-240Volt or 3-phase unbalanced.
But wire size and breaker must match element wattage.
If you have outlet, check the wire size and breaker, and check what other devices are drawing power from same circuit, then add up total watts and compare with charts on link below.
http://waterheatertimer.org/Color-codewire.html#water-heater

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

10-20-12
Circuit breaker is tripping on electric shower?

This could be absolute danger until more information is known.

1) Breakers trip because they sense heat, because the wire size is too small, or breaker size is mismatched with wire. Or breaker is loose on busbar.
Copy following links to determine correct wiring and breaker:
http://waterheatertimer.org/Color-codewire.html
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

GFCI circuit breaker will trip because of same heat condition described above, and also trip if ground fault is detected.
Water leaking into element will trip GFCI.
Absolutely you need to get this problem fixed before shower is put back into service.
Call electrician, or the installer, or the manufacturer, or all.
http://waterheatertimer.org/How-to-wire-GFCI.html#spa

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

I don't have specific suggestion for tankless tripping breaker or if that is a circuit breaker problem or a tankless problem.

1) Move wires to another same-size breaker and see if problem persists.

2) Compare amp draw on tankless label with wire size and breaker size amp rating.
For example 30 amp breaker using 10ga wire is rated for 80% of listed amps or 24 amps.

3) If you are drawing full 30 amps, then 30 amp breaker is getting hot. Breaker trips with heat. Older breakers can trip more easily.
http://waterheatertimer.org/How-to-replace-circuit-breaker.html

4) Before calling service technician, open following link for Bosch troubleshooting steps.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

5) Be sure to read manual for yearly maintenance requirements.

6) Add a tempering tank for incoming cold water problem.
http://waterheatertimer.org/Tempering-tank.html

7) All gas tankless brands can be repaired by homeowner for $330.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

1) Turn off power before touching water heater that is shorting or wet or was flooded.
2) Circuit breakers & fuses blow because of heat. A short will cause heat. Tighten screws on terminals inside box, listen for crackling sound/burning smell from loose-fitting parts.
3) Easy test for circuit breakers: move water heater wires to another same-size breaker. If same-size does not blow, then problem is breaker.
4) A short between fuse box and water heater could be gnawed electrical wire. Inspect wire.
5) Wires have size markings. 5500 watt water heater needs #10 wire. 4500 watt water heater needs #10 wire but can work with smaller #12 if distance is not long. See label on side of heater for wattage, voltage, etc. Element wattage is water heater wattage even with 2 elements.
http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html
6) Short inside water heater can be elements or thermostat. Open covers and inspect parts for burning. Screws should be very tight against copper wire. Sediment could fill bottom of water heater cause lower element to short.
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http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

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