Ruud Error Code 31: Inlet Water Filter

Severity
Warning
Type
digital display
Estimated repair cost: $100 — $350 (parts + labor)
Warning: Your Ruud tankless water heater has detected a possible blockage in the inlet water filter, which can cause the unit to shut down. This requires troubleshooting to restore hot water.

How to Fix Ruud Code 31

  1. Step 1: Locate the inlet water filter on your Ruud tankless water heater. It's usually near the cold water inlet pipe.
  2. Step 2: Close the cold water shut-off valve to the unit.
  3. Step 3: Carefully remove the filter housing and inspect the filter. If it's visibly dirty, rinse it thoroughly under running water. For heavy buildup, soak it in a vinegar solution.
  4. Step 4: Reinstall the cleaned filter and filter housing, ensuring a tight seal. Open the cold water shut-off valve slowly.
  5. Step 5: If the error code persists after cleaning the filter, or if you're uncomfortable performing these steps, contact a qualified HVAC technician for assistance.

How to Reset Ruud Code 31

  1. Turn off the furnace power switch, usually located on or near the unit.
  2. Turn off the circuit breaker for the furnace. Wait 30 seconds.
  3. Restore power at the breaker and flip the furnace switch back on.
  4. Set the thermostat to call for heat. If the error code returns after 2-3 ignition attempts, the fault requires repair.

Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.

What Does Ruud Error Code 31 Mean?

The '31' error code on your Ruud tankless water heater indicates a potential issue with the inlet water filter. This filter is designed to prevent sediment and debris from entering the unit and damaging its internal components, like the heat exchanger. When the filter becomes clogged, it restricts water flow, causing the unit to operate inefficiently or shut down completely. This can lead to inconsistent hot water temperatures or a complete loss of hot water. Ignoring this error can lead to scaling and mineral buildup inside the heat exchanger, which is a much more costly repair.

Common Causes

  • Clogged inlet water filter due to sediment or debris buildup
  • High mineral content in the water supply (hard water)
  • Debris from recent plumbing work
  • Damaged or deteriorated filter

Diagnostic Steps

If... Check Expected
Unit displays error code 31 Inspect the inlet water filter for visible debris or clogs Filter should be relatively clean and free of obstructions
Filter appears clean Measure the water pressure at the inlet with a pressure gauge while the unit is running Pressure should be within the manufacturer's specified range (typically 40-80 PSI)
Low water pressure at the inlet Check the main water supply pressure to the house Normal house pressure (40-60 PSI). If low, the issue is external to the tankless unit.

Applicable Ruud Models

Replacement Parts

Part OEM Number Est. Cost Where to Buy
Inlet Water Filter — — —
Inlet Water Filter Housing — — —

Related Codes on Same Models

Other codes that affect the same Ruud model families as 31.

Code Description Severity
11 No Ignition Critical
12 Flame Failure Critical
13 Improper Combustion Critical
14 Overheat / Thermal Fuse Critical
15 Inlet Temp Sensor Fault Warning
16 Outlet Temp Sensor Fault Warning
21 Air Supply / Operational Switch Warning
24 Flow Sensor Malfunction Warning
29 Condensate Neutralizer Issue Warning
33 Fan Motor Fault Warning