Navien error code 351 indicates an abnormal auto feeder valve issue or low system water pressure, which can typically be resolved by checking supply valves or resetting the unit.
Table of Contents
- What does error code 351 mean on a Navien tankless boiler?
- Why does my Navien boiler keep showing error code 351?
- How do you perform quick fixes for Navien error code 351?
- What are the next troubleshooting steps if the error persists?
- Which fix matches your specific Navien error symptom?
- When should you stop troubleshooting and call a professional?
- What information should you have ready before calling support?
- How can you prevent Navien error code 351 from coming back?
What does error code 351 mean on a Navien tankless boiler?
Error code 351 indicates an abnormal auto feeder valve or low water pressure in the closed heating loop.
When your Navien combi-boiler detects that the auto feeder valve has stayed open for too long or that the system water pressure is persistently low, it triggers error code 351 to prevent dry firing and internal damage. This code specifically points to issues within the automatic water refill mechanism.
- The internal sensor detects low pressure in the closed heating loop.
- The automatic water feeder valve has remained open for over five minutes.
- Water may be failing to refill the heating pipes properly.
- A leak in the system can prevent the pressure from rising normally.
- Exact error behavior can vary slightly across different Navien model lines.
Why does my Navien boiler keep showing error code 351?
This error is typically caused by a closed water supply valve, a leaking heating pipe, or a faulty auto feeder valve.
Understanding the root cause helps you determine whether you can fix the problem yourself or if you need professional assistance. Common triggers range from simple supply valve restrictions to mechanical failures in the automatic water refill assembly.
- The cold water supply valve leading to the auto feeder is closed or restricted.
- A hidden leak in your radiators, baseboards, or underfloor heating pipes.
- A defective or stuck auto feeder valve that fails to regulate water flow.
- A malfunctioning water pressure sensor failing to read correct loop levels.
- Overflow through the condensation hose caused by continuous over-filling.
How do you perform quick fixes for Navien error code 351?
Perform these initial safety and valve checks to restore proper water pressure.
Before attempting any troubleshooting, turn off the electrical power breaker to protect internal components. Verify that all external supply valves are fully open and clear of any blockages.
- Turn off the power breaker to the Navien unit before touching any internal components.
- Locate the incoming cold water supply valve and ensure it is fully open.
- Check the system pressure gauge to see if it reads below normal operating levels.
- Perform a manual system reset on the front control panel display.
- Observe the unit for a few minutes to see if the error code clears.
What are the next troubleshooting steps if the error persists?
Inspect the plumbing lines for leaks and check the auto feeder valve connection.
If simple resets and valve checks do not resolve the issue, you must inspect the broader heating network for leaks or electrical connection faults. Turn off the power before inspecting wiring or internal plumbing fittings.
- Unplug the appliance or turn off the breaker before inspecting internal wiring.
- Inspect all visible heating pipes, radiators, and fittings for signs of water leaks.
- Check the wiring harness connector on the auto feeder valve for loose pins.
- Manually verify if the auto feeder valve opens and allows water flow into the loop.
- Power the system back on to test if the pressure stabilizes.
Which fix matches your specific Navien error symptom?
Match your immediate observation with the corresponding corrective action in this reference table.
Different symptoms associated with error code 351 point toward distinct underlying problems. Use this quick reference guide to identify the appropriate response for your situation.
| Symptom | Likely cause / fix |
|---|---|
| Closed water supply | Open the inlet valve fully |
| Low pressure reading | Refill loop via auto feeder |
| Continuous water flow | Stuck feeder valve, replace part |
| Leaking heating pipe | Repair plumbing leak immediately |
| Unresponsive sensor | Test and replace pressure sensor |
When should you stop troubleshooting and call a professional?
Call a licensed technician if you detect gas leaks, electrical component failures, or internal heat exchanger damage.
Gas appliances and high-voltage electrical systems carry inherent safety risks. Stop working immediately if you smell gas, encounter sealed-system issues, or require internal component replacement.
- Stop immediately and call a licensed professional if you smell gas near the appliance.
- Contact a technician if internal electrical control boards or wiring harnesses are damaged.
- Call for service if the auto feeder valve needs to be replaced entirely.
- Seek professional help if the internal heat exchanger shows signs of leaking.
- Never attempt repairs on gas valves or venting systems yourself.
What information should you have ready before calling support?
Gather your exact model number, serial number, warranty details, and a summary of troubleshooting steps tried.
Having precise details ready when you contact manufacturer support or a service technician helps speed up diagnosis and ensures you receive accurate parts or warranty service.
- Locate the exact model number and serial number on the rating plate.
- Check your purchase date and warranty coverage status.
- Write down the exact error code number displayed on the screen.
- Note all troubleshooting steps and valve checks you already performed.
- Describe any unusual noises or leaks observed around the unit.
How can you prevent Navien error code 351 from coming back?
Prevent future occurrences by scheduling annual maintenance and monitoring system water pressure regularly.
Proactive maintenance helps keep your tankless boiler running efficiently and prevents unexpected pressure drops. Routine checks ensure that valves and sensors operate reliably throughout the year.
- Monitor the closed-loop pressure gauge on a monthly basis.
- Schedule annual professional maintenance and system tune-ups.
- Inspect heating pipes and radiator connections periodically for minor leaks.
- Keep the area around the boiler clean and clear of obstructions.
- Review your owner manual for recommended water quality testing guidelines.
Frequently Asked Questions
Can I manually fill my Navien boiler if error 351 appears?
Yes, many models feature a manual bypass or fill valve that allows you to add water to the heating loop. However, you should only do this if you have confirmed there are no active plumbing leaks. Over-pressurizing the system can lead to component strain or pressure relief valve discharge.
What should I do if the error code returns immediately after a reset?
If the error code returns right away, it usually means the underlying problem has not been resolved. The auto feeder valve may be stuck closed, or the system pressure sensor might be defective. Turn off the unit and contact a qualified technician for further diagnosis.
Is error code 351 dangerous to my home?
Error code 351 itself is a safety lockout designed to prevent the boiler from running dry and overheating. While the lockout protects the unit from catastrophic damage, ignoring persistent pressure losses can lead to heating failure and potential water damage from leaks.
Does this error affect domestic hot water or only space heating?
Error code 351 specifically relates to the closed-loop space heating side of a combi-boiler system. While it may shut down the unit to protect internal components, domestic hot water functionality can sometimes remain impacted depending on the exact model configuration.
How much does it cost to fix a faulty auto feeder valve?
Repair costs vary significantly depending on your geographic location, labor rates, and whether your unit is covered under warranty. It typically involves diagnostic fees plus the cost of replacing the auto feeder assembly or pressure sensor by a licensed technician.
Bottom Line
Start by turning off the power breaker, then inspect your incoming water supply valves and system pressure gauge. If adjusting the valves and resetting the unit does not clear error 351, contact a licensed professional for assistance.
Sources
- Navien Installation and Operation Manual
- Navien NCB Service Manual
- Manufacturer Support Page