Takagi Condensing Code 631
External pump fault. The external pump — a recirculation pump connected to the heater rather than built into it — is not behaving. On installations without one, this code should not appear.
Part replacementThe verdict
Replace a part
Often not a water heater repair at all: an external pump that has lost power, seized, or been switched off produces this. Check the pump before booking anything.
Typical cost: $0–$800
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the Condensing — not averaged across the brand.
Source: Takagi Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 13), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Find the recirculation pump and check it has power and that you can hear it running.
- Check the isolation valves on the recirculation loop are open.
- If the pump is dead or the code stays, book a service call.
Frequently asked questions
I do not have a recirculation pump.
Then the heater is configured as though you do. Say that when you call — it is a settings question rather than a hardware one, and it changes where the technician looks.