I just replaced my electric hot water heater. I think the coil burned out on the old one. I bought a Whirlpool 12yr and it has the "diagnostics" on it. I connected everything, filled it with water, then turned on the power... no green light.. no power. The line coming in has power. It runs off a 30 amp double breaker.. I used a simple tester (light for 110v or 220v).. and at the wires coming in I am getting a 110v light. The new heater and old heater are 240v only... is my tester wrong, or did something happen at the breaker? Or do I have a bad water heater? Help!

Judging the circuit breaker, you should have 240 volts at the water heater. Check your tester on a known 240 volt source to test your tester. If the tester shows 240 volts then the circuit feeding the water heater is faulty.

The problem can be the circuit breaker, or any splice in the circuit to the water heater.

If you find any of these conditions, and still need more infor get back with your question.

Go back to your installation instructions. Do they say anything about needing a neutral wire? Many heavy duty appliances, including ranges and dryers, have 110 components and are wired up with 3 conductor plus ground wire. The red and black wire are both 110 volt to ground, but opposite phase. The white is neutral and connected to ground. Older water heaters were wired with 2 conductor cable with a ground, but no neutral. Your test light should show 220 between 2 phases of 110, but 110 to ground from either.

If your new heater requires a neutral that the old one didn't have, you may have to run another wire, easier with singles in a conduit, and maybe a pain if you must snake new NM through walls. Post back with the details.

Thanks guys, it turned out I had a bad breaker and was only getting 80v at the heater.. new breaker, working great...