In our series on spa and hot tub error codes, we turn our attention today to the HOT messages that your topside control may be trying to give you.
OH, or 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, shutting off the heater, and turning on circulation pumps and blower 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, a high limit switch may be need to be reset on some spa packs; look for a red reset button. 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, it removes less heat, 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. The causes of low water flow in a spa include:
- Dirty spa filter cartridge
- Closed or partially closed valves or jets
- Pump has an air lock, or has lost prime
- Low water level in spa, skimmer sucking air
- Spa drain cover is obstructed or 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, which could fall out of calibration, or become too sensitive. Digital spas have electronic sensor circuits, which are more durable than mechanical switches, however temperature sensors, hi limit sensors, relays and circuit boards also 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 it’s 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.
OH, HH or HOT trouble codes, or a hot tub overheating is not usually a spa heater problem – it is almost always a flow problem, and when it’s not a flow problem, it’s a bad temp sensor, high limit 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, done with the spa heater and all systems powered Off, and only by someone 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 hi limit circuits for wire or plug or sensor problems.
Happy Hot Tubbin’
Hot Tub Works