Rheem Rheem RTGH-95DVLN Prestige 9.5 GPM Condensing Tankless Gas Water Heater 99 Error Fix: Communication Error — Remote Controller

Error code 99 on the Rheem Rheem RTGH-95DVLN Prestige 9.5 GPM Condensing Tankless Gas Water Heater means: Communication Error — Remote Controller. The main PCB has lost communication with the remote temperature controller or, in multi-unit installations, the cascade controller board. Check the communication wiring between the main unit and the remote controller — ensure connections are secure and wiring is not damaged. If using a multi-unit cascade system (multiple tankless heaters linked together), check the cascade controller and all inter-unit communication wiring. A standalone unit without a remote controller connected should not normally display this code — if it does, there may be a PCB fault or an incorrect DIP switch setting telling the unit to expect a remote controller.

The most successful fix is "Test and Replace Main PCB or Remote Controller Board" (hard difficulty, ~60 minutes). Estimated DIY cost: $15-$20. HomeMD has 2 community-ranked fixes for this error.

This error is rated warning severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Test and Replace Main PCB or Remote Controller Board") is rated hard difficulty and takes about 60 minutes. Tools needed: T20 Torx screwdriver, Multimeter, Needle-nose pliers.

DIY cost: $15-$20. Professional repair typically costs $250-$350. Many homeowners save money by trying the top-ranked community fix first.

The Rheem Rheem RTGH-95DVLN Prestige 9.5 GPM Condensing Tankless Gas Water Heater has 8 other known error codes, including: 05 (False Flame Detection), 10 (Abnormal Combustion — Blocked Vent), 11 (Ignition Failure — No Flame Detected), 12 (Flame Failure — Flame Lost During Operation), 14 (Thermal Fuse Activated — Overheat Safety), and 3 more.