Navien Error Code E736: Cascade communication fault (Boiler)
Navien error code E736 on a boiler means: Cascade communication fault. It is also called Navien diagnostic code E736.
Homeowner? What Navien code E736 means for you
Check, then call Your boiler is reporting: Cascade communication fault. 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 the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Look at the pressure gauge on the boiler. If it reads much lower than usual or near zero, or water is leaking, call a technician.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the boiler gas valve is open (handle in line with the pipe).
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and 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?
The main and sub boilers lost communication. Manual action: check the cascade cable.
Applies to: Navien NHB-H (NHB-055H/080H/110H/150H) and NFB-H fire-tube (NFB-175H/200H) condensing boilers
Common causes of Navien code E736
- Ready-Link cable loose or damaged at CNK1
- Sub unit not registered / IDs lost
- Sub unit powered off
Navien models that use code E736
NFB-175HNFB-200HNHB-055HNHB-080HNHB-110HNHB-150H
Other Navien Boiler codes
All Navien Boiler error codes →
Navien code E736: homeowner questions
What does Navien code E736 mean?
Cascade communication fault. The main and sub boilers lost communication. Manual action: check the cascade cable.
Is it safe to keep using my boiler 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 boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Boiler Not Heating: What to Check
Troubleshooting guides
- No heat or some zones cold All brands · Boiler
- Annual service checklist - Navien NHB-H Navien · Boiler
- No space heat - Navien NHB-H / NFB-H Navien · Boiler
- Relief valve discharging - Navien NHB-H / NFB-H Navien · Boiler
Source: Navien NHB-H Installation and Operation Manual, 11.14 Understanding Error Codes, p.119; Navien NFB-H Installation Manual, 11.7 Understanding Error Codes, p.116; NHB-H User's Information Manual (V1.0 Apr 2024), 5.2, p.24. 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.