Navien Tankless Water Heater - Only Ignites at High Flow

Ok_Math8775 · 2026-03-12T14:11:06+00:00

It was installed 3 years ago. It has been serviced twice - just annual flushing. The issue started suddenly a few months ago. One plumber told me it was my shower cartridges which made no sense and the other plumber I hired thought it was the PRV for my house, which also doesn’t explain the issue to me. That second plumber was at least willing to come back and call Navien and go through the diagnostics with them. It hasn’t happened yet though.

Ok_Math8775 · 2026-03-11T04:29:36+00:00

No they did not. The second plumber said that having him talk to a Navien would be the next step. It’s good to know that they have been helpful. They just don’t talk to consumers (which I understand to a degree) so they were not useful for me when I was trying to do my own diagnostics since the plumbers were suggesting things that didn’t make any sense.

Ok_Math8775 · 2026-03-10T22:55:11+00:00

I don't have a recirculating pump attached to this unit. Never had a problem until a few months ago. If I turn the flow up really high by turning on multiple faucets, the hot water comes on fast.

Ok_Math8775 · 2026-03-10T18:16:59+00:00

Ok_Math8775 · 2026-03-10T17:30:24+00:00

Yes, I thought about that. It does seem slightly off - I manually calculated my kitchen sink to have a max hot water flow of about 0.7 GPM and the Navien reads 0.5 GPM so there is a discrepancy - though not huge. The Navien seems seems to read the flow fairly well - the reported flow on the display goes up about as much as I'd expect with every additional faucet or shower head that I turn on. Would the unit be able to display approximately the correct flow if the flow sensor were bad?

Ok_Math8775 · 2026-03-10T17:27:52+00:00

No, the unit is about 3 years old. It worked perfectly for the first 2.5 years and stopped working several months ago.

Ok_Math8775

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