Navien E302: Low Water Pressure Error

The unit won't kick on at all, and E302 is the code sitting on the display — not because the water heater is broken, but because it isn't receiving the incoming water pressure it needs to even attempt a heating cycle.

Applies to: Navien NPE, NCB, and NHB tankless and combi/condensing water heaters

What it means

Low Water Pressure Error — incoming water pressure to the unit is below the required minimum. Tankless units generally need noticeably more incoming pressure and flow than a tank-style heater to activate reliably, so a pressure level a tank heater would never notice can still trip this code on a tankless one.

Most common causes

Shutoff valve not fully open
Municipal water supply issue
Clogged inlet water filter
Well pump problem

What you can safely check yourself

Check that the cold water shutoff valve to the unit is fully open
Clean the inlet water filter per the owner's manual
Check your home's water pressure with an inexpensive hose-bib pressure gauge

When to call a professional

House pressure is confirmed low at the main and needs a pressure-boosting solution, or the inlet valve/filter needs professional service.

Gas supply lines, gas control valves, and venting should only be worked on by a licensed plumber or HVAC technician. Mains/line-voltage electrical work should be done with the breaker off and, beyond a simple reset, by a qualified electrician or plumber.

What the fix costs

If the fix is simply opening a valve the rest of the way or cleaning the inlet filter, this one can cost nothing beyond your time. If your home's water pressure genuinely needs boosting — a well pump issue or a municipal supply problem — that's a separate plumbing job priced on its own merits, so get a dedicated quote rather than assuming it's bundled into the typical $150–$600 water heater service call (Angi, Fixr).

Related codes

All Navien codes

Every Navien water heater fault code — the full list on one page.

Sources

Navien NPE/NCB/NHB owner's manual and error code troubleshooting guide (manufacturer documentation)

This site is an independent reference, not a substitute for a licensed plumber or electrician. Gas water heaters can leak carbon monoxide, leak gas, or catch fire if serviced incorrectly. Anything involving the gas line, gas control valve, venting, or main electrical wiring should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.