Takagi T-H3 661 — Bypass Valve Fault (540h Only)
661
Bypass valve fault (540H only). The bypass valve faulted; inspect the bypass valve for connection or breakage of wires, locked motor drive due to scale buildup, and water leakage. The table classifies it as Error.
Applies to
This domestic hot water 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 DHW code involves the hot-water side: sensors, flow, the mixing/bypass valve or the DHW heat exchanger. It does not say whether the fix is a sensor, a valve or a flush.
Safe things to observe
- Note the code and whether the problem follows a hot-water draw or appears at all times.
Do not
- Do not open the appliance to test DHW components yourself.
How professional service helps
- A technician tests the DHW sensors, flow switch and valve circuits, and cleans the DHW path where the manual directs.
- 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.
Differential-pressure bypass valve
A differential-pressure bypass valve opens when system pressure rises — usually because zone valves have closed — so the boiler keeps enough flow to…
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
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.