Takagi T-H3 101 — Warning for the 991 Error Code
101
Warning for the 991 error code. A warning for the 991 error code; ensure the gas type matches, check the heater altitude DIP switches, intake and exhaust blockage, direct-vent terminal spacing, and grease or dirt in the burner and fan motor. The table classifies it as Error.
If you smell gas
- Stop what you are doing. Do not use phones, switches, matches or anything that can spark inside.
- Go outside and leave the door open behind you.
- Call the FortisBC 24-hour emergency line at 1-800-663-9911 or dial 911.
Only after that, call ROMA about the boiler. Official guidance: FortisBC gas leaks and odour.
Applies to
This gas-train fault code is displayed by the T-H3 control (built-in/remote controller and green LED flash codes) on T-H3 family models (T-H3-DV/OS, T-H3S-DV/OS, T-H3J-DV/OS and T-H3M-DV/OS in natural gas and propane; the manual covers the 140H, 240H, 340H and 540H models), as documented in Takagi T-H3 / T-H3S / T-H3J / T-H3M On-Demand Water Heater Installation Manual and Owner's Guide, doc 68A255-1, error codes section (models 140H, 240H, 340H, 540H) (68A255-1). Codes can differ between controller generations, so always check the manual that matches your unit.
- Takagi T-H3 Series
- Takagi T-H3-DV-N
- Takagi T-H3-DV-P
- Takagi T-H3-OS-N
- Takagi T-H3-OS-P
- Takagi T-H3S-DV-N
- Takagi T-H3S-DV-P
- Takagi T-H3S-OS-N
- Takagi T-H3S-OS-P
- Takagi T-H3J-DV-N
- Takagi T-H3J-DV-P
- Takagi T-H3J-OS-N
- Takagi T-H3J-OS-P
- Takagi T-H3M-DV-N
- Takagi T-H3M-DV-P
- Takagi T-H3M-OS-N
- Takagi T-H3M-OS-P
Controller: T-H3 control (built-in/remote controller and green LED flash codes). Source manual: 68A255-1.
Why a code is not a diagnosis
A gas-train code involves the gas valve or its electrical circuit. It does not mean there is a leak; the circuit, coils and wiring must be measured by a licensed technician.
Safe things to observe
- If you smell gas, stop, go outside and call your gas utility's emergency line or 911 before anything else.
- Note the exact code and what the appliance was doing when it appeared.
- Check whether other gas appliances in the building are working.
Do not
- Do not reset or run the appliance while the gas valve circuit is suspect.
- Do not touch the gas valve.
How professional service helps
- A technician verifies harness connections and coil resistances against the manual before replacing parts.
- 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.
Parts and service
Parts commonly involved
These parts appear in the documented text for this alert. A code reports a condition, not a failed part — a technician confirms the cause by testing before anything is replaced.
Combustion fan (blower)
The combustion fan is the sealed boiler's lungs: it draws in combustion air, keeps the burner's gas-air mixture correct, and pushes flue gases out…
What a technician checks →Burner assembly
The burner assembly is where gas and air meet and burn inside a boiler, and its condition decides whether combustion is clean or makes carbon…
What a technician checks →Vent terminal
The vent terminal is where a boiler's exhaust and combustion-air pipes meet the outdoors, and keeping it clear is one of the few combustion tasks a…
What a technician checks →Boiler venting (flue and air intake)
A condensing boiler vents cool, wet flue gases through dedicated plastic pipe that must meet ULC S636 in Canada and the boiler manufacturer's own…
What a technician checks →
Service for this alert
- Gas Boiler Repair
Licensed gas technicians from ROMA Heating & Cooling diagnose and repair residential and light-commercial gas boilers across…
Every boiler part explained — what it does, how it fails and what a technician checks.
Documented for Takagi T-H3 Series.
Frequently asked questions
Does this code mean I have a gas leak?
Not by itself. If you smell gas, stop, leave the building and call your gas utility's emergency line or 911 from outside before anything else. Otherwise the code points to a fault a technician confirms on site.
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-H3 / T-H3S / T-H3J / T-H3M On-Demand Water Heater Installation Manual and Owner's Guide, doc 68A255-1, error codes section (models 140H, 240H, 340H, 540H) · 68A255-1 · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.