As a professional repair technician, understanding the diagnostic codes displayed on the heater's control board is crucial for efficient servicing. These codes indicate specific operational or component faults within the unit.
You should be aware that installation and service must be performed by a qualified installer or service company. When troubleshooting, turning off the power supply before working on electrical components is an essential safety instruction.
If the numeric display shows a diagnostic error code, a quick initial step to try clearing the code is to press the MODE button to cycle the heater to STANDBY and then back to SPA or POOL. It is normal for the heater to delay up to 5 seconds before resuming normal operation after clearing a diagnostic error code this way, assuming the code does not immediately re-appear.
Below is a detailed breakdown of the Diagnostic Codes and their corresponding troubleshooting procedures:
Universal H Series Heater Diagnostic Codes and Troubleshooting
| Code | Description | Detailed Information and Troubleshooting Steps |
|---|---|---|
| AC | Blower Vacuum Switch closed | Information: This stands for "Air Switch Closed." The blower vacuum switch is closed when it should be open, preventing the control from starting the blower. Automatic reset is immediate once the switch opens. Troubleshooting: 1. Isolate the blower vacuum switch and test continuity between the terminals. 2. If continuity exists (closed when expected open), replace the switch (FDXLBVS1930). 3. If the blower continues to run while the heater is OFF (in STANDBY mode), replace the Integrated Control Board (ICB) (FDXLICB1930). |
| AO | Blower Vacuum Switch open | Information: The blower prover switch failed to close after the blower started, causing the control to stop the ignition trial and lock out (blower keeps running). It can also occur if the switch opens unexpectedly during operation; the control attempts a re-light, and if the switch doesn't close, it locks out. Automatic reset is immediate after the error is corrected. Troubleshooting: 1. Check for damaged blower wiring, blower vacuum switch wiring, vacuum tubing, and connections. 2. Verify the voltage selector plug configuration is correct for the incoming voltage. 3. Measure blower resistance (before Sept. 2010: 8–9 ohms; after Sept. 2010: 4–5 ohms). If out-of-range, replace the Blower. 4. When the heater is calling for heat, verify 110–125VAC is present across pins 1 & 2 of the Inducer plug on the ICB. If voltage is present and the blower is running, replace the Blower Vacuum Switch (FDXLBVS1930). If 110-125 VAC is not present, replace the ICB. |
| BD | Bad board or secondary high voltage fault | Information: This code covers several internal faults, including power-up errors, gas valve "ON" error (lockout, 2-minute auto-restart), gas valve "OFF" error (10 errors cause 60-minute lockout), and data retrieval errors (lockout). Troubleshooting: 1. Check the continuity of the FC4 Fuse. If the fuse is blown, proceed to the FC4 fuse troubleshooting section. 2. If FC4 is OK, test for 110–125VAC on the high voltage output (P6 connector pins 3-5 on the Fuse Board). 3. If voltage is present at P6, check for 110–125VAC input at the ICB (E10 connector pins 1-3). If voltage is present here, replace the ICB (FDXLICB1930). 4. If voltage was missing at P6, check the transformer output (P4 connector, grey wires) for 110-125VAC. If P4 is good, replace the Fuse Board (FDXLFWP1930); if P4 is bad, replace the Transformer (IDXL2TRF1930). |
| CE | Communication Error Between Control Module and Display Interface Assembly | Information: Communication between the ignition board (ICB) and the display board was not established within 3 seconds of power-up, or was lost for 30 seconds. The error clears upon a valid data exchange. Troubleshooting: 1. Cycle the electrical power OFF and ON to attempt to clear the error. 2. Inspect the display ribbon cable connection for security to the ICB. 3. If the error persists, replace the Display Interface Assembly and/or Key Pad (part number depends on model/date). 4. If the error still remains, replace the ICB (FDXLICB1930). |
| EE | EEPROM Error / Bad board | Information: An error was detected in the ignition control circuit board. Troubleshooting: Indicates a defective ICB board. Replace the ICB (FDXLICB1930). |
| HF | Flame present with Gas Valve not energized | Information: Flame is sensed when the gas valve is off (heater goes into lockout). The blower runs continuously until the error is corrected. Control automatically restarts 2 minutes after correction. Troubleshooting: 1. Power cycle the heater to try clearing an erroneous code. 2. Press the mode button to call for heat. Test for 24VAC off the gas valve during a call for heat. 3. If 24VAC is present but manifold gas pressure is NOT present (using a manometer), the gas valve is defective and requires replacement. 4. If 24VAC is not present or other conditions are met, replace the ICB (FDXLICB1930). |
| HS | Maximum return water temperature exceeded and/or rapid water temperature rise | Information: A) Inlet water temperature exceeds 104°F (40°C). B) Sensor reports a temperature change rate faster than 6°F (3.33°C) in 60 seconds, indicating potentially damaging low water flow. If condition B is detected 3 times in one hour, the heater locks out until power is cycled OFF and ON. Troubleshooting: 1. Verify adequate water flow. 2. Ensure the water inlet and outlet plumbing are not reversed, as reversed plumbing often causes frequent occurrences of this code. 3. Ohm the thermistor (temperature sensor) by checking resistance between the black wire and each red wire (readings should be the same, 10k ohms at 77°F). If the two readings differ by more than 1° or are significantly different, replace the thermistor (FDXLTER1930). 4. If the thermistor checks out, replace the ICB (FDXLICB1930). |
| IF | Ignition Failure | Information: The control exceeds the maximum number of ignition retries or recycles (3 retries, then waits 60 minutes and retries 3 more times). Heater shuts down and locks out. Automatic reset is 60 minutes. Troubleshooting: 1. Verify the main gas supply and the internal heater gas valve are in the ON position. 2. Ensure flame sensor and gas valve connections to the ICB are secure. 3. Verify gas static, load, and manifold pressures are correct. Manifold reading should be between 1.8"-2.0" w.c. for natural Gas or 6.8"-7.0" w.c for propane. 4. Test for 22–28VAC to the gas valve during ignition trial. If voltage is present, but no manifold pressure (use manometer), replace the Gas Valve. If VAC is not present, replace the ICB (FDXLICB1930). 5. Verify the correct flame sensor (5") is installed (especially important for models manufactured prior to 4/14/2009). 6. Inspect gas orifices and burner tubes for blockage and clean as needed. |
| IO | Igniter Circuit Open | Information: The control senses that the igniter circuit is open while the blower is running, leading to blower shutoff and lockout. Automatic restart occurs 2 minutes after the error is corrected. Troubleshooting: 1. Power down and inspect ignitor wiring for damage and ensure it is securely plugged into the ICB. 2. Measure ignitor resistance (must be 8–25 ohms between 20°–140°F). If resistance is out-of-range, replace the ignitor (FDXLIGN1930). 3. If resistance is correct, replace the ICB (FDXLICB1930). |
| LO | Water Pressure Switch, Vent Pressure Switch, or Temperature Limit Switch Fault | Information: "Limit Open." The limit string opens, causing heater shutdown and lockout. This code is NORMAL when the pump is turned off. Automatic restart is 2 minutes after the limit string closes. Troubleshooting: 1. Verify adequate water flow. If flow is insufficient, increase flow rate or clean the filter. 2. Water Pressure Switch (WPS): Test continuity across the WPS terminals while the pump is running. If open, replace the WPS (FDXLWPS1930). Adjust the switch if necessary. 3. Temperature Limits: Inspect and test continuity across the Temperature Limit Switches. If open or wires are damaged, replace the High Limit Kit (FDXLHLI1930). 4. Indoor Installations: Check the Vent Pressure Switch tubing/connections. Ensure the flue is not blocked or restricted. Test Vent Pressure Switch continuity. If open, replace the switch (FDXLVPS1930). 5. Exhaust Gas Limit (Heaters after Feb. 2016): Test continuity across the Exhaust Gas Limit Switch. If open, replace it (FDXLEGL1931). Note that this switch is a one-time safety and requires replacement after tripping, and the heat exchanger should be inspected. |
| PF | Voltage polarity reversed, low voltage detected | Information: Polarity Failure. This displays if 120V polarity is reversed, low voltage is detected, or the ground path is not sufficient. Reset is immediate after correction. Troubleshooting: 1. Verify incoming power is within 10% +/- of the required voltage. Correct any source power issues. 2. If 120 VAC, measure voltage between neutral and ground; voltage presence indicates reversed polarity. 3. Ensure both internal and external ground and neutral connections are clean and secured. 4. If all checks are acceptable, replace the ICB (FDXLICB1930). |
| SB | Keypad failure | Information: Stuck Button. A keypad button is closed (pressed) for more than 30 seconds. The error clears when the condition is corrected. Troubleshooting: 1. Test the resistance of the membrane switch buttons on the ribbon cable. 2. When the button is not pressed, resistance should be greater than 100 Mohms. When pressed, resistance should be less than 100 ohms. 3. If readings are incorrect, replace the display/bezel/keypad assembly. |
| SF | Temperature Sensor (thermistor) input failure | Information: Sensor Failure. Occurs due to an excessive temperature difference (5°F or more) between the two thermistors, or if both sensors are "out of bounds" (less than 10°F or greater than 180°F). Automatic restart is 2 minutes after correction. Troubleshooting: 1. Inspect the thermistor wire and secure connections to the ICB. 2. Measure resistance between the black wire and each red wire (resistance should be the same, 10k ohms at 77°F). 3. If the readings differ by more than 1° or are significantly different, replace the thermistor (FDXLTER1930). 4. Otherwise, replace the ICB (FDXLICB1930). |