Hello: It sounds like a volt-ohm meter is called for. Test (or have tested) power coming into the heater. It should be 240 VAC. If you have only half of that, try flipping both breakers fully off than on again. Most electric heaters are 240 volts and have two breakers… you may have reset only one of them. It sounds like once you get 240 volts at the heater, you’ll be back in hot water 😉
Yours, Larry
ps. it would be interesting to know why the breaker tripped in the first place. You might check for any leaks to ground in the elements. That process is described in other posts.