Ruud Error Code 79 — Causes & Fix

Ruud water heater error code 79 indicates a leak detection alert — the unit's water sensor has detected water in the drain pan or sensor area. As with Rheem-branded equivalents, Ruud code 79 may automatically shut off heating as a protective measure to prevent worsening damage if the cause is a tank leak.

What triggers Ruud code 79

Ruud Achiever Plus, Pro Hybrid, and other newer models include a moisture sensor that monitors for water presence. The sensor reports to the control board, which displays code 79 and (depending on configuration) shuts off elements/burner to prevent additional water heating during a potential leak scenario.

Critical first action

Code 79 means water is present where it shouldn't be:

1. Close the cold water inlet valve to the unit
2. Open a hot fixture to relieve tank pressure
3. Visual inspection of the unit to find the water source
4. If active leak from tank wall: tank failure — replacement required
5. If from T&P discharge, drain valve, or fittings: localized fix

Common leak sources to inspect

• Tank wall (under insulation): water trails down the side from internal corrosion through the glass lining. Tank failure — replacement required.
• T&P relief valve discharge: water from the T&P discharge tube indicates either thermal expansion (no expansion tank) or T&P failure
• Drain valve seep: visible water at the drain valve location. Tighten or replace.
• Inlet/outlet fittings: dielectric unions or piping connections that may have loosened
• Anode port: if recently serviced, gasket may not be sealing — retape and retighten
• Condensate (Pro Hybrid models): heat pump condensate drain blockage causes overflow

Pro Hybrid heat pump specific considerations

Ruud Pro Hybrid (heat pump water heater) produces 1–3 gallons of condensate daily during heat pump operation. Code 79 on a Pro Hybrid is often condensate drain blockage rather than a true tank leak. Inspect:

1. Condensate pan at the unit base
2. Condensate drain line for kinks or blockages
3. Condensate pump (if equipped) for operation
4. Routing — line must run downhill the entire path

Sensor reset procedure

After identifying and resolving the water source:

1. Dry the sensor area thoroughly
2. Restore cold water supply (if previously shut off)
3. Verify no leaks at all connections under pressure
4. Reset the leak detection by power cycling the unit or pressing the specific reset button (location varies by model)
5. Monitor for 24 hours — verify code doesn't return

False alarm scenarios

• Recent maintenance (water spilled during service): dry and reset
• High ambient humidity in install closet: verify the sensor isn't reading condensation as a leak
• Sensor failure: rare but possible. If sensor reports water when none present, sensor replacement may be needed

When tank wall leak is confirmed

Tank wall leaks cannot be field-repaired. The glass lining has failed at one or more points, allowing steel corrosion through to the exterior. Once this happens, the leak only worsens. Replacement is required regardless of warranty status. If under warranty, file the warranty claim immediately — replacement tank shipping typically takes 1–2 weeks.

Water damage to surrounding spaces

If code 79 led to water damage in surrounding finished areas:

• Document everything with photos before cleanup
• Contact homeowners insurance for sudden-discharge water damage claim
• Begin drying immediately to prevent mold growth (24-48 hour window)
• Replace the failed water heater as quickly as possible to prevent additional damage