Whirlpool 40 gallon energy smart elecrtic water heater. The control board binks once, by the panel means system start up failure,but we still have hot water,but every time we use the hot water it starts blinking. hitting the reset button does not help, it seems once the tank is full again it resets itself.What could be the problem?

Order from Whirlpool using the serial number located on label side of tank.
The 6 year warranty has probably expired.
You can save money by converting to regular water heater.
http://waterheatertimer.org/How-to-convert-energy-smart-water-heater-to-ordinary-water-heater.html

Since the energy smart that is pictured is older than 6 years, it means the anode rod is probably depleted and tank hull has probably started to rust inside.
Catch up on the maintenance while you are working on the heater and you can prolong life almost indefinitely.
http://waterheatertimer.org/How-to-maintain-water-heater.html

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

Control board can be bad...
Resources on following two links:
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html
http://waterheatertimer.org/How-to-convert-energy-smart-water-heater-to-ordinary-water-heater.html

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

Probably.
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html
Manuals, troubleshoot, and contact information on link above

Gene

Water Heater Timers Save Money

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

http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html
Older style or newer?
5 flashes on older unit indicates lower element is bad.... so maybe the control board is bad
Test your old element for continuity
http://waterheatertimer.org/How-to-test-water-heater-element.html

http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#new
Was tank full of water before power was turned on?
Gene

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

1) Bad thermostat or thermistor depending on model.
Whirlpool/Craftmaster/American energy smart has control box on top, and you can order parts from Whirlpool.

2) Copy following links to help identify product.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html

3) Add a comment with more detailed information:
You have electric water heater.
Unknown brand, possibly energy-smart.
Unknown control box.
Cut off? Do you mean 'reset' is tripped?

4) Whirlpool energy smart requires 10 gauge wire and 30 amp breaker.
Control panel may not function with undersized electric supply.
Control panel has blinking-light errors ... if no error code then maybe the control box is bad.

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

1) Copy following links for whirlpool energy smart resources:
http://waterheatertimer.org/pdf/Energy-Smart-troubleshooting-guide.pdf
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html

2) Control box is probably bad.
There are 2 types of control boxes for older-style energy smart water heaters.
You will need model number and serial number from label on side of tank to order from Whirlpool.

3) This older-type energy smart water heater is probably discontinued by AO-Smith, American, State, Craftmaster, Reliance water heater group that makes Whirlpool and Kenmore water heaters.
New generation energy smart offers interface with home automation and/or non-existent smart grid.
Older energy smart only offered potential interface with non-existent smart grid.

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

Water heater is not 100% identified.
Unknown if this is gas or electric heater.

Problem posted under Whirlpool water heaters typically made by American water heater company.
Call Whirlpool 877-817-6750.
They will ask for model number and serial number located on label on side of tank.
Call is answered in USA by trained person who can answer specifics about that model, including warranty, age, regular maintenance, error codes, and possible solution for that specific model and serial number.
I have found these folks to be helpful.

Whirlpool manuals do not show that specific model:
http://www.whirlpoolwaterheaters.com/support/manuals.aspx

If you have the energy smart electric water heater with electronic control board, then error code explanation shows on the control board. Error 1 or a single flash, is start-up failure and requires tank to be full of water. Read page 10 of manual. Make sure water heater is full of water and water is coming full stream out of tub spout before turning on power. Also disconnect power from unit, make sure water heater is full, and then reconnect power to see if unit resets.
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html
http://www.whirlpoolwaterheaters.com/downloads/6510306.pdf

1) Residential water heaters are non-simultaneous. Only one element works at a time.
Upper element comes on until top of tank is heated, and then lower element is switched on until lower part of tank is heated. Lower element keeps tank hot during standby hours
http://waterheatertimer.org/How-it-works.html

2) Typical Whirlpool energy smart has 4500Watt elements. Look at label on side of tank
If both elements were ON, that would draw 9000Watts or 37.5 amps, requiring 50 amp breaker and 8 gauge wire. V x A = Watts.
All dual-element tanks are 240V.
Whirlpool energy smart requires 10 gauge wire and 30 amp breaker so electronics are not starved during operation. If your wire or breaker are undersized, that is suspect for repeated failure.
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html

3) Typical electric water heater heats 21 gallons per hour. First hour delivery is higher since elements heat water as you use it. Overall however, electric water heater cannot re-heat as fast as gas because gas water heater burner carries more BTU punch per minute than electric element. Gas heats about 41 gallons per minute, with higher first hour delivery.

4) IF YOU HAVE OLDER energy smart and installed newer board, then you could have non-simultaneous operation is reversed so that lower element comes on first.
Read following post at Fixya:
http://www.fixya.com/support/t8263226-our_water_heater_doing
Contact Whirlpool 1-877-817-6750

5) Another potential problem is that you have sediment inside tank and that is reducing efficiency of lower element.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
http://waterheatertimer.org/How-to-test-water-heater-element.html

Add a comment with your experience so others with same-similar problem can benefit.

Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

I've worked on these before and most of the time it is the computer board which goes bad. I would check to make sure that my connections at the heater are good and that you have power up to that point. If you do then the board is bad and you will have to contact whirlpool.