What could be the problem when red ligth is flashing on the hot water tank control?

That's an atmospheric vent gas water heater with Honeywell gas control valve thermostat
Following links have information, error codes and troubleshoot manuals:
http://waterheatertimer.org/Honeywell-gas-valve-blinking-4-times.html
http://waterheatertimer.org/troubleshoot-gas-water-heater-thermostat.html#thermostat
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html

The only way to determine this is to have the tank inspected. If it is not too corroded then fix the control valve. If your water heater is only a couple of years old I would just call it good and replace the control valve without worries. It may still be under warranty

Is the control that operates the pump located in the storage tank? If so the pump not be pumping. A few factors might be needed to solve the issue.

You have tank-type water heater, but type of water heater and control is not known.
For possible help, add a comment and say if you has gas or electric water heater and describe what type of gas valve or control box is giving the error code.
Open following link to identify some basic types of controls:
http://waterheatertimer.org/How-to-adjust-temperature-on-water-heater.html

More information is needed.
Open following link to help identify your gas valve and access error code.
http://waterheatertimer.org/How-to-adjust-temperature-on-water-heater.html

Add a comment and say which gas valve matches.
Then add what code is blinking for possible help.

Upvote the help.
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The evidence points to a control malfunction.
Call Whirlpool for assistance: 1-877-817-6750
You will need your model number and serial number located on label on side of tank.
Serial number is required because models change as the technology evolves.

Open following link to read product details about the Energy Smart, and download typical manual.
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html

Note: Energy Smart water heater requires 10 gauge wire and 30 amp breaker.

Typical energy smart manual shows: 1 flash is start-up error, which indicates 'Power ON with no water in tank.'
This is not possible because at least the upper element would burn out, if not both elements.
If upper element burns out, this water heater will not make any hot water, since it is wired for ordinary non-simultaneous operation.
There cannot be air inside the tank since your hot water faucet is not spewing air.
http://waterheatertimer.org/How-it-works.html

Also be aware that model numbers change.
Read following account of fellow who replaced control board on his 4-year-old energy smart, and how he discovered wires are reversed on newer control boards. Be sure to ask Whirlpool about this possibility, in the event they say control board is faulty and send you new board:
http://www.fixya.com/support/t8263226-our_water_heater_doing

Tanks are marked with Hot and Cold.
1) If water connections are on top of tank, look for red marking or word HOT that shows where hot water pipe connects. Look for blue marking or word COLD that shows cold water connection.
2) If water connections are on side of tank, cold water connects to bottom one, and hot connects to top.

3) If hot and cold are reversed, the tank will not work.
Pipes on top of tank: cold water enters tank and is sent to bottom of tank in a long tube called the dip tube. This means the cold is on the bottom since hot water rises to the top. The hot water exits top of tank.
Pipes on side of tank: You want cold water to enter bottom, so hot water naturally rises to the top outlet.

For images and product information
For manual


You checked ohms, did you check for 240V across lower element when lower element is turned on?

Energy smart electric water heater has a control box on top of unit. Water heater does not have typical thermostats that can be tested and replaced. Temperature sensors located above each element send information to control box through small black and red wires. Temperature sensor sells for about $40, but there is no test listed that shows how to determine when sensors fail.

Potential problems:
-Temperature sensor is not reading correct temp
-Control box not processing correct temperature information
-Selector on control box set to 2, 3 or 4
-Thermostat temp on control box set lower than 120 degrees F
-Sediment build-up starting to surround lower element so water doesn't circulate (see if drain valve runs full-open

needs new thermostat(s) If the whole tank is heating( next time it trips, before using any hot water check the lower tank thru the lower element access(breaker off) If the lower tank is hot-you need a new lower thermostat. if just the upper part of the tank is heating -you need an upper thermostat.

This faucet is the hot only version so it has two copper lines and one Santoprene rubber line. The copper line directly under the handle is the inlet from the wall - the second copper line attaches to the hot water tank by the corner. The Santoprene line attaches to the middle of the hot water tank. This faucet cannot be installed without the hot water tank.