A 3-year-old Rinnai RU199i tankless water heater intermittently fails to ignite with Code 11, even after replacing flame rods and checking filters, and the problem recurs unpredictably.

Standard troubleshooting steps (rod replacement, cleaning) work temporarily but fail to resolve the root cause; diagnostic codes alone cannot pinpoint the intermittent failure mode, and no guided, step-by-step diagnostic tool exists for this specific issue.

Severity

4High

Willingness to Pay

implied

Added

Jun 2, 2026

Workarounds Described

removing and reinstalling flame rods to temporarily fix the issue
shutting down the unit for minutes/hours to reset it
posting diagnostic code data on Reddit for help

Implied Software Gaps

App that interprets diagnostic codes and guides the user through a decision tree to isolate the root cause of intermittent ignition failure
App that tracks repair attempts and recurrence patterns to recommend permanent fix

App Concept

Tankless Troubleshooter AI

An interactive diagnostic app for HVAC technicians and homeowners that uses device diagnostic codes, symptom history, and step-by-step logic to pinpoint the root cause of intermittent failures in tankless water heaters. Unlike static manuals or forum posts, it learns from patterns and suggests targeted tests to resolve recurring issues.

Key Features

Input diagnostic codes and symptoms to get ranked probable causes
Guided troubleshooting workflow with photos and videos
Log repair history and track recurring failures over time
Notify user of known recalls or service bulletins for the specific model

Target Users: Homeowners and HVAC service technicians dealing with Rinnai (and other brands) tankless water heater issues, especially those with intermittent failures.

Revenue Model: $9.99 per diagnostic report or $4.99/month subscription for unlimited access

Existing Solutions Mentioned

Rinnai diagnostic codesreplacement flame/igniter rodsblowing air into burner chamberchecking water inlet filterchecking air filter

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