What does the code Ec on my oasis hot tub mean? It flashes on and off between that the temperature.

Means "Economy"

You probably have a Balboa Control System.
Find the "Code" number on the label of the unit and do a Google Search. Find how to switch between Economy and Standard.
I recommend that spas be on Standard.

But if the spa is hot and is not giving you any problems, and the only irritant you have is not knowing what EC means, you can leave it alone, since you now Know.

Good Luck

Check your filter cycles and switch spa into Standard Mode as you have it in Economy. (In Economy mode it will only heat during the filter cycles).
If the Ecn or Ec Message is Alternating with the Water Temperature on the Display, the Spa is Operating in the Economy Heating Mode.

If the Ecn or Ec Message is ON Solid (Not Flashing) on the Display, the Spa is Operating in the Economy Heating Mode, but there is No current water temperature because the Spa is between Filter Cycles.

Ecn or Ec is Alternating with Temp:
The Spa is Operating in the "Economy" (Ecn or Ec) Heating Mode.

The Water Temperature is Sampled Only during Programmed Filter Cycles. The Heater will Only operate and Heat up to Set Temperature during the Filter Cycles. The Water Temperature will probably drop Below Set Temperature between Filter Cycles. Other Heating Modes are Standard, Standard in Economy, and Sleep Modes.

Ecn or Ec is ON Solid (Not Flashing):
The Current Water Temperature is "Unknown" (- - - or - -) while in Economy or Sleep Mode.

Between Filter Cycles, while in the Economy or Sleep Heating Modes, the Pump has not turned ON and the Last Water Temperature is not Current. To read the Current Water Temperature, either Change to Standard Heating Mode or turn On the Heating Related Pump, and wait at least 2 Minutes.

Your spa is in Economy Mode:
Ecn or Ec MessageEcn or Ec Message

If the Ecn or Ec Message is Alternating with the Water Temperature on the Display, the Spa is Operating in the Economy Heating Mode.

If the Ecn or Ec Message is ON Solid (Not Flashing) on the Display, the Spa is Operating in the Economy Heating Mode, but there is No current water temperature because the Spa is between Filter Cycles.

Ecn or Ec is Alternating with Temp:
The Spa is Operating in the "Economy" (Ecn or Ec) Heating Mode.

The Water Temperature is Sampled Only during Programmed Filter Cycles. The Heater will Only operate and Heat up to Set Temperature during the Filter Cycles. The Water Temperature will probably drop Below Set Temperature between Filter Cycles. Other Heating Modes are Standard, Standard in Economy, and Sleep Modes.

Ecn or Ec is ON Solid (Not Flashing):
The Current Water Temperature is "Unknown" (- - - or - -) while in Economy or Sleep Mode.

Between Filter Cycles, while in the Economy or Sleep Heating Modes, the Pump has not turned ON and the Last Water Temperature is not Current. To read the Current Water Temperature, either Change to Standard Heating Mode or turn On the Heating Related Pump, and wait at least 2 Minutes.

Ecn or Ec Message
Ecn or Ec Message

If the Ecn or Ec Message is Alternating with the Water Temperature on the Display, the Spa is Operating in the Economy Heating Mode.

If the Ecn or Ec Message is ON Solid (Not Flashing) on the Display, the Spa is Operating in the Economy Heating Mode, but there is No current water temperature because the Spa is between Filter Cycles.

Ecn or Ec is Alternating with Temp:
The Spa is Operating in the "Economy" (Ecn or Ec) Heating Mode.

The Water Temperature is Sampled Only during Programmed Filter Cycles. The Heater will Only operate and Heat up to Set Temperature during the Filter Cycles. The Water Temperature will probably drop Below Set Temperature between Filter Cycles. Other Heating Modes are Standard, Standard in Economy, and Sleep Modes.

Ecn or Ec is ON Solid (Not Flashing):
The Current Water Temperature is "Unknown" (- - - or - -) while in Economy or Sleep Mode.

Between Filter Cycles, while in the Economy or Sleep Heating Modes, the Pump has not turned ON and the Last Water Temperature is not Current. To read the Current Water Temperature, either Change to Standard Heating Mode or turn On the Heating Related Pump, and wait at least 2 Minutes.

in the economy mode it will only maintain a temperature so that it will not freeze. Economy mode is mostly for vacation time or for winter if you are not going to be using the hot tub for an extended period of time.
Put it into the standard mode and you will be able to have a HOT tub and will function as it should

US Parts Center

EC stands for Economy mode. This is a setting that tells the computer to check the temperature of the spa less frquently, as well as running fewer filter cycles. Spas should be set to EC while you are away on vacation or not planning to use it for a while

the Ec message is reffering to the mode the tub is set for. Ec stands for Economy mode. In Economy mode the heater will only come on during the filter cycle you have programmed. It will take a while for the tub to actually heat up in this mode. Change the mode to St mode which stands for Standard mode. Your manual should explain how to do this. usually you hit the temp button then the light button to change from mode to mode. Once the St is in the read out window don't touch anything and it will except the programmmed entry automatically. In the Standard mode the tub will keep heating until the set temperature is reached. then it will come on every half hr or so to check that the temperature is maintained.

Diarmait --
Technical Service Manual for the SubZero 600 series can be downloaded at:
[https://docstore.fedex.com/subzero]
Username=subzero
Password=subzero
Write back if you still need help.
-- SWT

EC stands for Economy. Change the mode until you reach ST and then it will stop flashing and function as normal.

Economy mode only allows the heater to function when the hot tub is on its filtration cycle.

Regards,
Ian.
http://hottub.synthasite.com