Error codes on the display: ER-03 and other control unit messages

Short answer: ER-03 means the control unit is not receiving a signal from the temperature sensor and therefore switches off the heating for safety reasons. In most cases the cause is a loose, damp or corroded sensor plug. The fix: switch off the power, check the plug and reconnect it, switch the power back on, reset. If the error returns, the sensor or cable needs replacing. Below is the full procedure, the related codes and the rules for doing this safely.

How the safety mechanism works

The control unit regulates the heating element based on the water temperature measured by the sensor. If that signal drops out, the unit can no longer monitor whether the water is overheating. It therefore switches off the heating and displays ER-03. The message is not a fault in the element itself, but a safety mechanism doing exactly what it should.

Fixing ER-03, step by step

1. Switch off the power. Switch off the circuit for the tub; never work on the unit with the power on.
2. Locate the sensor plug. The temperature sensor is usually located in or near the pipe of the element; the plug is on the control unit. The installation manual for your version shows the exact location.
3. Check for moisture and corrosion. Disconnect the connector and inspect the pins: green or white deposits indicate corrosion, droplets indicate moisture. Dry the connector and gently clean the contacts.
4. Inspect the cable. Look for kinks, damaged insulation, signs of gnawing or a pinched cable. Have a damaged cable replaced; a makeshift repair is not an option in a wet environment.
5. Reconnect until the connector clicks audibly or you can feel it lock into place.
6. Switch the power back on and reset according to the unit's manual (usually: switch the unit off and back on after a minute, or use the reset button).
7. Test. Let the pump circulate and check whether the unit displays a water temperature and switches on the element.

Related error messages

Flow is the common factor behind most of these messages: resolve a low water level, a full filter or an incorrect valve position first; see backwashing the sand filter and hot tub not heating up.

Resetting safely: the fixed rules

• Only reset after you have removed the cause; resetting blindly only bypasses the safety mechanism.
• After an overheating message (ER-02), let the water and element cool down first.
• Do not reset more than once; if the message returns, it is a service matter.
• Never open the control unit with the power on, and leave any wiring work to a certified installer.

Preventing moisture

Most sensor and communication faults are caused by moisture in connectors. Prevention:

• Keep the technical compartment or panel dry and closed; check seals every season.
• Route cables so that water cannot run along the cable into the plug (a small drip loop under the connector).
• After changing the water or winterising, check the connectors before switching the power back on.

When to call service

• The message returns after one correct reset.
• The cable or sensor is visibly damaged.
• There is water inside the unit or display.
• Multiple codes appear at once, or a code that is not in the manual.

Note the exact code, the model and year of manufacture, when the message occurs (while heating, when switching on, after rain) and take a photo of the display; see requesting service.