Correct Tech, Inc. - Quality Spa Controls and Equipment

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Using CT975 Printed Circuit Board 


No display at topside

Check miss-wire fuse between J38 and J18 – If blown, check

Incoming wiring L1, L2, N are correct

Check that connection to main board is clean and sound at J30

Test a new topside control.

 Check for 120V primary power going into the transformer and for 12V secondary power out of the transformer to J35 & J34 on the board before replacing the transformer.

Replace board if there is 12V to J35 & J34

  Display flashes " th1 / 39 " or “ - - - / 39“ on system start up

If the fill water is less than 39F it will stay in freeze protect mode until over-ridden or the water temp rises above 39F 

( see freeze protect information )

Check that temperature sensing probe connection to main board is clean and sound at location J2.

Try new temperature sensing probe.

Display fl ashes " th2 / current temperature " or “- - - / current temperature “on system start up.

Check that the temperature sensing probe connected to the main board is clean and sound at location J1.

Try new temperature sensing probe

Display flashes " th2 / 39 " or “ - - - / 39” on system start up

This indicates that both thermisters are detecting tub water temperature of less than 39F / 4C or they are both disconnected (open). Pump(s) and blower will run in this condition.

Display flashes " OH "  or the “ Current Temperature" ( OVER HEAT )

This indicates that the spa water temp is over 112F. The system should be shut down in this state and will re-start automatically when the water cools below 112F.

Display flashes " hot " or the “ Current Temperature “ ( OVER HEAT )

This indicates that the heater body is over 112F. The system should be shut down in this state and will re-start automatically when the water cools below 112F.

Display flashes " HL " or “ Current Temperature” ( HIGH LIMIT )

This indicates that either the heater or the spa has reached 118F or higher. The system will not re-start automatically.  To re-start the system, the water temperature must be below 112F and the heater key at the topside control must be pressed.

Display flashes " HL / 210" ( THERMISTER SHORT )

This indicates that one of the thermisters is shorted out causing a cross between the two terminals at J1 or J2. 

Erratic operation or 0 at topside panel

 Check  for proper connection at J30

Shut off system and restart

Check for debris inside topside panel control housing

 Check cable connection at the topside control remove, clean reconnect

 Try new topside control

Replace main board  

No heat

 Check the topside control for " HL". This indicates that the system has overheated. Make sure the temperature has fallen to less than 112F and press the heat key or turn the power off and back on again to reset.  

Check that temperature set point is higher than actual tub temperature.

Check for flashing LED at topside control to indicate heat demand

Check that filters are clean


Check to see if the pilot light at the equipment panel is on. This indicates if power is actually getting to the heater element. If this light is on and there is still no heat, the element should be checked for continuity. If the element is open, it needs to be replaced.  


If the pilot light does not turn on, then the pressure switch may need to be adjusted. The pressure switch is located on the heater body and has a small wheel on it. This wheel should be turned counter clockwise to allow the heater to run on less water flow / pressure. This pressure switch is a protection switch that is meant to turn the heater off if the pump fails to operate or if there is not enough pump pressure. A test to see if the pressure switch has been adjusted correctly is to unplug the circulation pump and see if the heater shuts off. It should operate again when the pump is plugged back in. The heater should not be allowed to operate under static (gravitational) pressure when the pump is not on as it will cause an instant overheat.

 If a flow switch is used it must be checked for continuity when closed.

·    Note : Some systems have fixed pressure switches to prevent tampering. It is highly recommended that the spa plumbing is checked for obstructions first.

If these remedies do not work the power will have to be checked from the element terminals back to the power source at the main input power terminal. This must be done with a voltmeter checking for voltage at each connection from the heater element back through the relays to the main power as a process of elimination.

The power should be checked at the coil side of the relay. If there is power at the coil side of the relay and the relay is not closed (allowing power to pass through the power terminals), and then the relay must be replaced.

Temperature readout is wrong

Remove temperature sensor / thermister from the tub location and submerge it directly into the water. This will verify if the sensor has been installed where ambient air has affected it or it is defective.


 If the water is too hot and the high limit has tripped, the water must be allowed to drop to less than 112F before it will reset. Reset by pressing the heat key at the topside control or restarting the system.

The circulation of the water may be too low, allowing the heater body to overheat. Be sure that all valves are fully open to allow maximum water flow over the heater element and that there are no flow obstructions.

  If the LED at the topside panel is not flashing and the spa is still heating, then the heater relays may be welded shut. This can be checked by making sure that the temperature set point is lower than the actual spa temperature and then checking that there is no power going to the coil side of the relay. If there is no power at the coil and there is power passing through the relay power terminals, then you know it is welded shut. A further test to this is to tap the relay to see if the internal " tack weld " frees up. In the event that there is not a replacement relay readily available, this may work temporally until a new relay can be installed.

The friction and radiant heat from the pump motor can cause an extremely high ambient temperature around the spa and the equipment causing an overheat condition. If this condition is suspect, try running the spa with the equipment door off to see if it still overheats. Some software will shut the low speed pump off if the temperature creeps 2 degrees F above the set point. This will not affect a circ pump.

Pump(s), Blower or light does not shut off

System may be in freeze protect mode if water is less than 52F

( this temp level may vary with custom software ) System will run in protection mode and you will not be able to control pumps, heater or optional blower. You must introduce warm water into spa or manually over-ride the system or wait for the system to heat up on its own. Depending on outdoor temp this can take several hours.

Try new topside control

Replace main board

Circulation pump does not work

Check the fuse and power connections.

Circ pumps are not powered through the circuit board and will remain on in board power or internal board failure to prevent possible freezing. 

Light does not work

Check bulb

Check for 120V into transformer and 12V out to light

Check topside control for light function

Filter cycle does not operate

Adjust the temperature set point to be within 2 degrees F of the actual  water temperature. If the water temperature creep 2 degrees F higher than the set temp, the system will shut off to allow the water to cool. When the water cools down to the desired set point, filtration will resume. Proper ventilation of the equipment will minimize this.

Ground Fault Interrupter Trips

Check if it does it only when heat turns on, if so check element by removing the power to the element terminal and turn the heat on. If it only faults when the element is connected with power, the element has a ground fault and must be replaced.

Check the element for possible leak or condensation at bulkhead. 

This test can be done with the pump(s), blower, ozonator, or any other peripheral equipment as a process of elimination to see where the fault may be.

Be sure that the neutral on the GFCI has been wired properly in the main panel.


All connections should be checked that they are secure.

Always exercise general electrical common sense for safety.


Please do not hesitate to contact us if you have any questions or concerns.

Correct-Tech, Inc.

Correct Tech, Inc. - the user friendly control company


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