Rinnai Water Heater Air Pressure Switch Replacement Guide — What This Part Does
The air pressure switch (also called a vent-proving switch) closes a safety circuit when the inducer fan creates enough airflow through the combustion chamber and exhaust vent. The control board waits for this signal before opening the gas valve and firing the igniter. If the switch does not close, the unit displays Code 10 or a combustion-air fault and shuts down to prevent unsafe ignition conditions.
The switch itself can fail from normal wear, debris in the pressure-sense tube, or a stuck diaphragm. However, most Code 10 faults trace back to blocked intake or exhaust vents, improper vent installation, a weak or dead fan motor, damaged wiring harnesses, incorrect DIP switch settings for gas type, or heat-exchanger blockage. The pressure switch is only one link in the chain, so diagnosis must rule out airflow, fan, and control-board issues before replacing the switch.
Signs It Needs Replacing
- Code 10 or combustion-air error on the display The unit flashes Code 10 and refuses to ignite, indicating the control board did not receive the vent-proving signal from the pressure switch before attempting ignition.
- Fan runs but igniter does not fire You hear the inducer fan spin up normally, but the main burner never lights because the safety circuit is open at the pressure switch.
- Repeated lockouts after a power cycle The heater attempts a start sequence, runs the fan briefly, then shuts down and locks out again without ignition.
- No continuity across switch terminals when fan is running With the fan on and creating airflow, a meter shows infinite resistance or open contacts at the switch, confirming the switch is not closing.
- Intermittent ignition failures on cold starts The unit sometimes lights and sometimes faults, suggesting a marginal switch or loose connector that breaks contact under vibration.
- Recent vent work or wind-driven exhaust issues A pressure-switch fault often appears after vent modifications, termination clearance changes, or windy weather that disrupts draft.
How to Replace It
- Turn off electrical power to the water heater at the circuit breaker and close the gas shut-off valve at the unit.
- Close the cold-water inlet valve and open a hot tap downstream to relieve line pressure.
- Remove the front service panel to access the control board, fan motor, and pressure switch assembly.
- Locate the pressure switch near the fan or on the left side of the combustion chamber (a small round or rectangular device with a rubber or plastic pressure-sense tube running to the inducer or heat exchanger).
- Photograph or label the two electrical connectors on the switch terminals, then pull the connectors straight off.
- Disconnect the pressure-sense tube from the barbed nipple on the switch body (twist gently and pull, or release the clamp if present).
- Remove the single mounting screw or clip holding the switch to its bracket, then lift the switch free.
- Install the new pressure switch on the same bracket and secure it with the original screw or clip.
- Push the pressure-sense tube firmly onto the nipple (or install a new tube if the old one is cracked or kinked) and secure with a clamp if required.
- Reconnect the two electrical terminals in the original positions, open the cold-water and gas valves, restore power, and observe a start cycle to confirm the fan runs and the unit ignites without a Code 10 fault.
The Part You Need
| Part | Notes |
|---|---|
| Rinnai air pressure switch / vent proving switch | Amazon | Find your exact part number on the model and serial plate inside the front cover, then cross-reference with Rinnai or an authorized parts supplier. Some models use a combined bi-switch or safety-circuit assembly, so verify the switch configuration for your unit. |
| Pressure-sense tube (if damaged or kinked) | Amazon | A short length of flexible high-temperature rubber or silicone tubing that connects the switch to the inducer housing or heat exchanger. Replace if cracked, kinked, or clogged with debris. |
When to Call a Pro
Call a qualified gas-appliance technician if you are unfamiliar with combustion-air circuits, if the fan motor does not run at all, or if Code 10 persists after replacing the switch and inspecting the vents. Professionals have manometers to measure actual draft pressure, continuity testers for the wiring harness, and factory service bulletins for DIP-switch configuration and heat-exchanger inspection. Gas-fired tankless heaters also require proper vent termination, clearances, and combustion testing that are difficult to verify without training and tools. If you see soot, smell gas, or suspect a heat-exchanger crack, shut down the unit immediately and call for service. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.