Purpose
Diagnostic procedures for tankless water heater issues.
When to Use
- Intermittent hot water, error codes, no hot water, or performance issues with a tankless unit
Common Issues
Error Codes
Check unit display — reference manufacturer manual
Navien 110-01: exhaust blockage — check for water in vent from back pitch, ensure 1/8" pitch, check hangers every 4ft
Navien 003: ignition failure — check gas supply, igniter, flame rod
Navien 012: flame loss — check gas pressure, flame rod, venting
Document error code in ServiceTitan with photo of displayNo Hot Water
Check power and gas supply
Verify minimum flow rate is met (0.5-0.75 GPM to activate)
Check inlet filter/screen for debris
Verify gas line is properly sized for BTU demand
Check igniter and flame rodIntermittent Hot Water
Check recirculation system if installed
Verify unit is properly sized for peak demand
Check for crossover between hot and cold linesCondensate Issues
Check condensate drain line for clogs
Ensure proper routing — not draining to unapproved location
Check for frozen condensate lines in winter
Ensure line is insulated or routed to prevent freezingVenting Issues
Inspect all vent connections for proper seal
Check pitch — condensate must drain back to unit
Verify termination clearances from windows, doors, gas meters
Look for bird nests, debris, or ice at terminationStandard Tankless Diagnostics
Check inlet water pressure and flow rate
Descale heat exchanger if performance degraded (recommend annual)
Clean inlet filter
Check gas pressure with manometer
Inspect flame pattern through viewing windowImportant Notes
- Tankless units are more complex — call supervisor if unsure
- Condensate drainage is now a standard diagnostic step
- Check manufacturer warranty before recommending repair vs. replacement
- Annual descaling is a great maintenance upsell
Related SOPs
- Water Heater Diagnostics Flowchart — for tank units
- CO Testing After Water Heater Install — post-install requirements
