Takagi T-D2 391 — Air-fuel Ratio Rod Failure
391
Air-fuel ratio rod failure. The air-fuel ratio (AFR) rod failed; check for connection or breakage of wires and soot on the AFR rod. The table classifies it as Error.
Applies to
This fault code is displayed by the T-D2 control (7-Seg LED and remote controller error codes) on T-D2 models (T-D2-IN-N, T-D2-IN-P, T-D2-OS-N, T-D2-OS-P), as documented in Takagi T-KJr2 / T-K4 / T-D2 On-Demand Water Heater Installation Manual and Owner's Guide, doc 62S051-1, fault analysis of error codes (T-D2 models) (62S051-1). Codes can differ between controller generations, so always check the manual that matches your unit.
Controller: T-D2 control (7-Seg LED and remote controller error codes). Source manual: 62S051-1.
Why a code is not a diagnosis
The code reports the condition the control detected; the underlying cause must be confirmed on site by a licensed technician using the manufacturer's procedure.
Safe things to observe
- Note the exact code, when it appears and what the appliance was doing.
- If the appliance has stopped, call a technician rather than repeatedly restarting it.
- If you smell gas, stop, go outside and call your gas utility's emergency line or 911 before anything else.
Do not
- Do not ignore a code that returns after a reset.
How professional service helps
- A licensed technician diagnoses the cause with the manufacturer's test procedure.
- Combustion and safety devices are verified with an analyser and the manufacturer's procedure after any repair.
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Frequently asked questions
Can I clear this code myself?
Clearing a code without fixing its cause usually just brings it back. Note the code, check the safe items on this page, then call a licensed technician. If your appliance manual describes a user reset for this exact code and it stays away, no call may be needed.
Boiler locked out? Call with the alert text ready.
The brand, model and this alert are passed along when you request service online, so the technician arrives prepared.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
- Takagi T-KJr2 / T-K4 / T-D2 On-Demand Water Heater Installation Manual and Owner's Guide, doc 62S051-1, fault analysis of error codes (T-D2 models) · 62S051-1 · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.