I have a 2004 great lakes hot tub with a balboa controler. My hot tub heats up fine when the pump runs on high but the temp light never comes on when the pump runs in low.

Check the thermocouple on the water pipe.

First, balboa does not manufacture hot tubs! They make control systems for hot tubs. If you are no longer able to switch between modes, then your topside control panel buttons are dead or falling. But... Even if you are still in economy mode, spa should still heat up. Once a demand for heat is recognized, you have a "Heat Call" and heater should come on. Is the "heat on" light, illuminated? If so, water should be heating, if not heater element may be bad? A multi meter would be good here: is there proper voltage at terminals on circuit board to heater? If so, bad element! If no voltage, then heater is not necessarily bad, probably just fine, I would then look at sensors? Good luck

Balboa Direct has an excellent error code listing on their site.

Your problem is going to be in the circuit board in the spa control box under the skirt.
You have a bad relay.
Rod
US Parts Center

have you cleaned your filter recently. Sound like there may be a low flow error in low speed
either that or the start capacitor on your pump is bad and the pump will not come on in low speed unless you first give it a boost in high speed
anytime you ask for heat with insufficient flow there will be an error message

If the system is the Jacuzzi 52221-05 system mentioned in the subject header, there could be a stuck relay causing the problem and you might need to get a spa technician out to assist you in repairing the problem. However...

If it is a Great Lakes system as mentioned in your message body, then there could be a programming issue allowing the filter cycle to run continuously. Provide a model number off of the Balboa control. Then we can provide you an instruction manual or reference card to assist you in resolving this problem. you can also search our online manuals at our website. You can find them online at:

BALBOA WATER GROUP INSTRUCTION MANUALS

Contact Balboa's Customer support department directly at 800-645-3201, follow the prompts to customer tech support (or press 0 and ask for customer support). You will need to be at the spa, control panel open and ready to read off the chip number, and you will need to be proficient with a test meter (AC voltage). The SN error is related to a bad sensor(s), but can also indicate a failed board. An incorrect sensor set will also create this problem, so confirm you used the exact or compatible replacement. If the SN code issue is no longer a problem, but the spa is still not heating, look and see if the heater led is on. If it is, you likely have some burned relays on the board, which can be replaced cheaper than replacing the board. If you need more help, email me at [email protected]

press temp button and then the light button in sequence.