Navien boiler has no hot water and shows T High error
When a combi boiler provides central heating but no hot water through the taps—often accompanied by a circulation flow rate warning like the Navien T High error—the unit fails to switch over or heat the water properly. This leaves households completely without hot water until the flow restriction or sensor issue is resolved.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Doing a hard restart by turning off the system and unplugging it for about 10 minutes
- 2Feeling the supply and return pipes to check for warmth
- 3Checking valve positions on the recirculation lines
- 4Turning the heating on and off a few times to see if the diverter valve frees up
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“boiler in the picture is allowing heating to work but i’m not getting any hot water through the taps and when the heating is switched off the boiler temperature wont rise”source ↗
“Hello I’m looking for help on how to check my Navien NF-250/200H that currently has no hot water. The display is showing a message stating T High check the boiler circulation flow rate. Any way I can trouble shoot this before I call a tech?”source ↗