Spa & Hot Tub Error Codes - OH, OHH, OHS
In our series on spa and hot tub error codes, today we turn our attention to the HOT messages that your topside control may be trying to give you.
OH, OHH or OHS (overheat) all mean that a temperature sensor has detected unsafe water temperatures of 108° - 118° F, and your spa is in an emergency cool down mode. The heater is shut off, and the circulation pumps and blower are turned on to help dissipate heat.
Open the spa cover to allow excess heat and steam to escape. The spa obviously should not be used when OH or OHH is flashing on the topside control; as the water could be scalding hot for several more minutes. After the water cools, the high limit switch may need to be reset on some spa packs. Press any topside button to reset a digital spa after the water has cooled to 100° F.
What Causes a Spa to Overheat?
Low water flow (LF, FLO), is the usual cause of an overheating (OH, OHH) spa or hot tub. When water doesn't flow fast enough through the heater, the heater stays hotter, and the temperature of the water increases. Eventually, the temp sensors or high limit switches will detect the increased water temperature and shut everything down. Some causes of low water flow in a spa include:
- A dirty spa filter cartridge.
- Closed or partially closed valves or jets.
- The pump has an air lock, or has lost prime.
- Low water level in spa, and skimmer is sucking air.
- The spa drain cover is obstructed or a pipe is blocked.
What Else Causes a Spa to Overheat?
If your water flow is perfectly fine, then you could have a problem with the thermostat or high limit switches used on older spa packs. These can sometimes fall out of calibration or become too sensitive. Digital spas have electronic sensor circuits, which are more durable than mechanical switches. However, temperature sensors, high limit sensors, relays and circuit boards will still eventually fail on modern spas.
In most cases, for newer spas anyway, the water flow problem can be quickly remedied and the spa will cool, reset and start again on its own. Some panels need a prompt from you to restart. For spas without digital controls, you may need to manually reset the high limit switch near the heater housing.
Spa Overheating Troubleshooting Flow Chart
Here's a Cal Spa troubleshooting flow chart that has some other possible triggers of seeing OH, OHS, OHH or HH blinking on your spa panel. Open the spa cover and let the spa cool down for 10 minutes, then touch the control panel to reset the circuits, or push a red reset button on air systems.
For OH, HH or HOT trouble codes, an overheating hot tub is not usually a heater problem. It is almost always a flow problem. When it's not a flow problem, it's usually a bad temp sensor, high limit switch or a stuck relay.
Here's another Cal Spa troubleshooting flowchart for spa error codes OH, including testing the spa heater element for excessive resistance. This type of testing should only be done with the spa heater and all systems powered OFF, and only performed by someone who is qualified to test safely.
So, the next time your spa throws you a OH, OHH or some other "overheat" error code, you know what to do. Clean or replace the spa filter, open all the jets and turn the pump on high. If you still have problems, check over your temp sensor and high limit circuits for wire, plug or sensor problems.