Breaker is tripping off every 20 min i know amp are right plz adviced me how to fix

Replace the limit, by tripping often they become even more likely to nuisance trip.

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

1) Not likely the timer is problem, unless there was fire or overheating in timer box. Use nose and eyes to inspect for signs of high heat.

2) Eliminate timer as suspect:
Move wires on timer to test if timer relays have gone bad.
Move terminal 4 to terminal 3
Move terminal 2 to terminal 1
http://waterheatertimer.org/How-to-wire-T104-Intermatic-timer.html#T104

3) Check watt rating of Hayward pump, and voltage.
1Hp motor at 240Volt draws 8 amp, and can draw 6 to 8 times that amount when starting. Up to 100 feet, should be at least 12 gauge wire and double-pole 20 amp breaker. Over 100 feet, 10 gauge wire and 30 amp double-pole breaker is best.
http://waterheatertimer.org/Color-codewire.html#motor

4) Intermatic T104 240V timer is rated 40 amps
Can safely handle 1 Hp motor without nearing heat-rating capacity of timer

5) Make sure the motor is wired correctly for 240Volts.
If motor is wired for 120, and 240 is applied, then tripped breaker can result.

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

It could be element shorted to ground through steel tank, so don't touch tank when breaker is ON.
Or you have undersized 12 gauge wire and 20 amp breaker and the heat has loosened breaker on the busbar. Breaker trips when heat exceeds breaker limit. Jiggle breaker and listen for crackling sound.

To restore hot water now:
Turn off circuit breaker, and open top cover then Push in reset button on top of heater to restore functionality. Put back insulation and factory cover.
To fix water heater: test and replace bad element.
http://waterheatertimer.org/How-to-test-water-heater-element.html
If problems continue
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#trip-breaker
http://waterheatertimer.org/Troubleshoot-household-electricity.html

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

Breaker trips when heat on wire exceeds amp rating, or when breaker is bad.
Most breaker are slow acting, and do not trip immediately.
Shorted elect could cause problem.
http://waterheatertimer.org/Water-heater-is-tripping-breaker.html

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

Is this breaker connected to water heater?

1) A double 20 amp breaker is called a 240Volt breaker.
20 amp breaker is actually rated for 16 amps for safety margin.
It is also important that this breaker have 12 gauge wire which is color-coded yellow.
Look at label on side of water heater for wattage of unit.

2) For example 4500 Watt water heater is typical.
4500 watts divided by 240Volts = 18.75 amps which is nearly full capacity for the 20 amp breaker, and is slightly above the safety margin.
http://waterheatertimer.org/B220C.html

3) If breaker is getting old, and it works at full load each time water heater is on, it can wear out.
Open circuit breaker box and replace breaker:
http://waterheatertimer.org/How-to-replace-circuit-breaker.html

4) You can also move circuit breaker wire to another same-size breaker and see if problem continues.

Add a comment for more free help.
Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on timer or any do-it-yourself project.
Fixya is always less expensive than a service call.

The Rheem water heater uses 4500 Watt elements
Check label on side of any appliance to see electrical rating details
2 element tank with two 4500 watt elements is still a 4500 watt appliance since both elements are never ON at same time.

Volts x amps = watts
amps = watts divided by volts

amps = 4500 divided by 240Volts or 220Volts
amps = 18.75
Your water heater uses 18.75 amps to 20.45 amps

Your 25 amp breaker should only carry 80% of rated value
25 amps x 80% = 20 amps.

So your water heater breaker is correctly sized.
You should have a 10 gauge wire going to this water heater.
12 gauge wire is a bit undersized for 4500 Watt water heater
Feel the water heater wire to see if it is warm.

If the main breaker is getting hot when 20 additional amps are being used by the water heater.
1) The house is using more amps than your 100 amp main can carry
Using the formula, 100 amps x 80% = 80 amps for the main breaker
Add up your total amp draw.
For example if your 3500 watt oven is ON, it draws 16 amps.
If your 5000 Watt electric heater is on, it draws 23 amps.
Your 1500 Watt 120V microwave draws 12.5 amps.
Add these numbers up plus your water heater, and it comes to 71 amps.
71 amps is getting close to the max 80 amp, but it's not over.
Now if you have a pool pump and and hot tub and a table saw going, the main breaker could be overdrawn.

2) To solve the problem short-term, you can put a timer on the water heater and use it only when needed.
http://waterheatertimer.org/Compare-13-electric-water-heater-timers.html

3) The main breaker is bad and needs to be replaced.

If you need help figuring circuits or timers, add a comment and I will help

If it ran for more than 5minutes prior to this problem, then it's probably not the breaker.
The water heater is 9000 watts and at 240volts should draw around 37amps. Fuse/breaker should be ~1.25X the current so the breaker amps is around 46, but they don't make that one. So 50 ?
The problem is related to the heating elements since that's about the only thing that could gradually trip the breaker.
My guess.