We just bought a new water heater and it's not heating up water.

If your electric hot water heater is slow to heat, runs out of hot water faster than it used to, or doesn't deliver any hot water at all, there's a 90 percent chance that simply replacing one or both of the heating elements will solve the problem. Water heater repairs are straightforward, and replacement elements are inexpensive ($8 to $20) and readily available at home centers, hardware stores and appliance parts dealers.
We'll show you how to test the heating elements, remove one if it's bad, and install a new one. Just keep in mind that water heaters have a typical life span of 10 to 15 years. If your heater is approaching old age, replacement may be smarter than repair

Did they turn the power off to the heater before you bought the house?
Check there first. I used to shut the power off to ours when going on vacation. Check curcuit breaker if its hydro and if its gas make sure the the gas is turned on and pilot is lit.

Th easy fix would be installing a new heating element that has burned out. You don't say what size this tankless heater but if it stopped working entirely you might have just one heating element inside. You can test it by (1) turning off the circuit serving the heater, disconnecting one of the wires to the heating element, then taking an ohmmeter to see what the resistance of the element is. If it is "infinity" then it is open and burned out. Replace element. If it is around 6 ohms (for a 10kW heater running at 240V) then the heating element is OK. Unfortunately those heating elements don't last forever. Check the repair manual on how to replace the heating element.

1) Test elements, and if elements check out, then replace both thermostats.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#new
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#warranty

2) Add a comment with result.

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Doesn't sound like its the dip tube, its a element problem, I would contact bw directly to see if heater is stil in warranty and they will send you new parts free.

Hi,

The next thing you need to do is find out whether you have 240v to the bottom element....the top will not heat till the bottom is satisfied...
An electric meter is critical when working with these units....trace the power and see where it stops....

here also are some tips that will help you...

Electric Water Heater Wiring Diagram
Electric Water Heater not Working
heatman101

No , white and black to either or. (White - Neutral) (Black- hot)

Check the elements, if you have access to a meter to check them. If they are getting power to elements and you have no hot water.
The elements are not working correctly. I had some elements check out ok till the thermostat's turned on and the elements didn't heat.
Sounds like the elements are bad.

Every electric water heater I have ever installed makes a low hum while heating. I believe this is a combination of the current going through the elements and the minerals in the water cooking on the elements. That is the best explanation I have. Hope this helps.

I would say then the heating element has a resistive short to ground. The 1.98m Ohm reading is high, but not high enough -- should be infinite. I would say replace heating element... And, when you install new one, make sure there is no water leaking thru heating element cavity and ensure area around cavity is clean & "in order".

How old is water heater?

Charlie