Navien Error Code E736: Cascade communication abnormal (Tankless)
Navien error code E736 on a tankless water heater means: Cascade communication abnormal. It is also called Navien diagnostic code E736.
Homeowner? What Navien code E736 means for you
Check, then call Your tankless water heater is reporting: Cascade communication abnormal. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Safe things you can check yourself
- Check that gas reaches the house: other gas appliances work, or the propane tank is not empty.
- Make sure the heater is plugged in and its breaker is on. In winter, keep the power on: it protects the unit from freezing.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the hot and cold water valves under the heater are fully open.
- If you have a remote controller, turn it off and on once. If the code comes back, call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Navien error code E736 mean?
Units in a cascade are not communicating.
Applies to: Navien NPE-A2 (built-in recirculation) and NPE-S2 condensing tankless water heaters: NPE-150S2, NPE-180A2/S2, NPE-210A2/S2, NPE-240A2/S2
Common causes of Navien code E736
- Ready-Link cable loose or damaged
- IDs not assigned / unit removed
- Cascade protocol mismatch with older NR/NP/NPE units
Navien models that use code E736
NPE-150S2NPE-180A2NPE-180S2NPE-210A2NPE-210S2NPE-240A2NPE-240S2
Other Navien Tankless codes
All Navien Tankless Water Heater error codes →
Navien code E736: homeowner questions
What does Navien code E736 mean?
Cascade communication abnormal. Units in a cascade are not communicating.
Is it safe to keep using my tankless water heater with code E736?
It depends on the cause. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Can I reset Navien code E736 myself?
You can try one reset (power off for 30 seconds, then on). If Navien code E736 comes back, the cause is still there and a licensed technician should check it.
Who can fix Navien code E736 near me?
Aurora Star Tech Inc. repairs Navien tankless water heaters in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Tankless Water Heater No Hot Water: What to Check
Troubleshooting guides
- No hot water All brands · Tankless Water Heater
- Water temperature fluctuates All brands · Tankless Water Heater
- Hot water slow to reach fixtures - Navien NPE-2 Navien · Tankless Water Heater
- Hot water turns cold - Navien NPE-2 Navien · Tankless Water Heater
- No water from hot tap - Navien NPE-2 Navien · Tankless Water Heater
- Water not hot enough or too hot - Navien NPE-2 Navien · Tankless Water Heater
Source: Navien NPE-A2/S2 User's Information Manual (20049624A), 5.2 Understanding Error Codes, p.18. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.