Annual Tankless Water Heater Maintenance Checklist & Flush Schedule

Why This Matters: Regular maintenance extends the life of your tankless water heater by 5-10 years and prevents costly repairs. Most manufacturers require annual flushing to maintain warranty coverage.

Recommended Frequency: Flush annually (every 12 months). If you have hard water (above 10 grains per gallon), flush every 6-9 months.

Annual Flushing Checklist

Turn Off Power & Gas/Electric: Shut off the circuit breaker (electric units) or gas valve (gas units). Wait 10 minutes for unit to cool.

Close Water Valves: Close the cold water inlet valve and hot water outlet valve (isolation valves on either side of the unit).

Attach Flush Kit Hoses: Connect service port hoses from your flush kit to the unit's service valves. Place the pump and bucket below the unit.

Prepare Descaling Solution: Fill bucket with 4 gallons of white vinegar (preferred) or manufacturer-approved descaler. For heavy scale buildup, use commercial descaler (follow dilution instructions).

Open Service Valves: Open both hot and cold service valves on the unit. Ensure hoses are secure.

Run Flush Pump: Turn on the submersible pump and circulate the solution through the unit for 45-60 minutes (90 minutes for heavy scale). Check for leaks.

Rinse with Fresh Water: After flushing, replace vinegar with fresh water and circulate for 5-10 minutes to rinse out residual solution.

Close Service Valves & Disconnect Hoses: Turn off pump, close service valves, and carefully remove hoses. Have a towel ready for drips.

Clean Inlet Filter Screen: Remove and rinse the cold water inlet filter screen (usually located at the cold water inlet). Check for debris and sediment.

Inspect Air Intake & Exhaust (Gas Units): Check for blockages, nests, or debris in the air intake and exhaust vents. Clear if needed.

Reopen Water Valves: Open cold water inlet and hot water outlet isolation valves fully.

Restore Power & Test: Turn on power/gas, open a hot water tap to purge air, and verify unit fires correctly. Check for error codes.

Recommended Tools & Supplies

Flush Kit: Submersible pump, two 6-foot hoses, 5-gallon bucket
Descaler: 4 gallons white vinegar or commercial descaler
Tools: Adjustable wrench, screwdriver, towels
Safety: Gloves and safety glasses

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⚠️ SAFETY WARNING: Always turn off power and allow unit to cool before servicing. Gas units require proper ventilation. If you smell gas, shut off the gas supply immediately and call a professional.

Maintenance Log

Unit Information: Brand: ______________ Model: ______________ Install Date: ______________

Date	Service Performed	Next Service Due	Notes

Filter Cleaning Schedule

Frequency: Every 3-6 months (more often in areas with sediment or well water)

Turn off cold water inlet valve and relieve pressure by opening a hot water tap.

Unscrew filter housing cap (located at cold water inlet). Remove filter screen.

Rinse filter screen under running water. Use a soft brush to remove debris (do not use wire brush).

Inspect O-ring for damage. Replace if cracked or worn (O-ring kit available at hardware stores).

Reinstall filter screen and tighten cap hand-tight. Reopen cold water valve slowly and check for leaks.

Troubleshooting: Common Error Codes

Error Code	Problem	Solution
11 / 111	Ignition failure (gas units)	Check gas supply, ensure gas valve is open, verify power supply. Call technician if persistent.
12 / 112	Flame failure	Check for blockages in burner or exhaust. Verify gas pressure. May require professional service.
10 / 110	Air supply or exhaust blockage	Inspect intake and exhaust vents for obstructions, nests, or ice. Clear blockages and reset unit.
14 / 140	Overheating / thermal fuse	Unit overheated. Check for scale buildup (flush immediately). Verify proper water flow. Reset after cooling.
16 / 160	Over-temperature protection	Outlet water temp exceeded safe limit. Reduce temp setting, check for scale buildup, verify flow rate.
71 / 710	Solenoid valve circuit issue	Gas valve or solenoid malfunction. Power cycle unit. If error persists, call professional service.
90 / 900	Combustion abnormality	Check air supply, exhaust vent, and gas pressure. Clean burner assembly. May require technician.
79 / 790	Blocked drain or condensate	Check condensate drain line for blockage. Clear drain and neutralizer (condensing units only).

Note: Error codes vary by brand. Consult your owner's manual for brand-specific codes. Rinnai uses 2-digit codes, Navien uses 3-digit codes.

When to Call a Professional

Persistent error codes after troubleshooting
Gas leaks or burning smell (shut off gas immediately)
Water leaks from the unit
Unusual noises (banging, whistling, rumbling)
Inconsistent water temperature or no hot water
Heavy scale buildup requiring deep cleaning