UH Series Heater
First, verify the source power issue.
Check if the voltage selector plug is correct.
Inspect wires and connections for any damage.
Test the FC1 and FC2 fuses for continuity.
If the incoming power is correct and the fuses are not blown, proceed ...
Ensure the correct voltage selector plug is installed.
Inspect the transformer wiring for damage.
Measure the transformer resistance between specified wires.
If the resistance is out of range, replace the transformer.
If the problem persists, contact...
Check the remote connection and high limits for damage.
Inspect the low voltage wiring and water pressure switch wiring.
If any wiring is damaged, replace the wire harness or the specific component.
Test the gas valve wires for continuity against...
Inspect the ignitor and blower wiring for damage.
Measure the resistance of the ignitor and blower.
If the resistance is out of range, replace the faulty component.
For models manufactured before September 2010, measure the blower resistance across...
The 'BD' code indicates a bad board or secondary high voltage fault.
Power down the heater and check the FC4 fuse for continuity.
If the fuse is blown, replace it.
Verify the voltage across specified pins on the fuse board and ICB.
Replace the ...
The 'EE' code indicates a defective ICB board, which should be replaced.
The 'CE' code may clear with a power reset.
If the error persists, inspect the display interface ribbon cable and ensure it is securely attached.
Replace the display interface...
The 'IO' code indicates an ignitor circuit open.
Inspect the ignitor wiring and verify the ignitor ohm resistance.
If the resistance is out of range, replace the ignitor.
The 'SB' code indicates a stuck button, which may require replacing the display...
The 'SF' code indicates a sensor failure.
Check the thermistor resistance between specified wires.
If the readings differ by more than 1°, replace the thermistor.
The 'HS' code indicates high water temperature.
Ensure the water inlet and outlet...
Verify that the incoming power is within 10% of the required voltage.
Inspect the ground and neutral connections for cleanliness and security.
If the connections are secure and the voltage is correct, replace the ICB.
The 'HF' code indicates heat or flame sensed when the gas valve should be off.
Power cycle the heater and test for 24VAC off the gas valve.
If 24VAC is present and manifold pressure is not, replace the gas valve. Otherwise, replace the ICB.
Verify adequate water flow and inspect the water pressure switch wiring.
Check the continuity of the water pressure switch.
If the switch is open, replace it.
Inspect and test the high limits and vent pressure switch.
Ensure the main gas supply is on and the gas valve inside the heater is in the 'ON' position.
Verify the flame sensor and gas valve connections.
Check the inlet and manifold gas pressures.
Replace the gas valve or ICB if necessary.
The 'AC' code indicates the blower vacuum switch is closed when expected to be open. Test for continuity on the blower vacuum switch. If continuity exists, replace the switch. If the blower continues to run with the heater off, replace the ICB.
The 'AO' code indicates the blower vacuum switch is open.
Check the blower vacuum switch wires and vacuum tubing for damage.
Verify the voltage selector plug and measure the blower resistance.
Replace the necessary components based on the findings...
Press the 'MENU ICON' button to place the heater in 'STANDBY'.
Press and hold the minus button and 'MENU ICON' button for 3 seconds.
'bo' should appear on the display when the heater has successfully entered bypass mode.
Press the 'MENU ICON' button to place the heater in 'STANDBY' mode.
Press and hold the minus and plus buttons for 3 seconds.
Adjust the temperature using the minus or plus button.
Finalize by pressing the 'MENU ICON' button until the heater returns...
The minimum flow requirement varies by model, with a maximum water flow of 125 GPM. Flow less than the minimum can cause issues such as dry firing or boiling water, while exceeding the maximum can damage the heat exchanger.
Remove the black metal trim plate and water connection side upper end cap.
Disconnect unions from plumbing and remove hex head bolts.
Remove the water manifold to expose the heat exchanger tubes.
Inspect for damage from aggressive water chemistry...
Potential failure causes include low pH, high sanitizer levels, annealed fins due to low water flow, freeze damage, high pH, alkalinity or calcium hardness, and sooted conditions from improper fuel and air mixture.
Measure the inlet static pressure and load pressure.
Adjust the manifold pressure at the gas valve if necessary.
Ensure the inlet gas pressure meets the requirements set forth by the data plate on the heater.