Ignition Failure
🔎What the code means
The heater won’t fire after three ignition attempts (111). It will clear itself when water flow stops or power is cycled.
NG 111 failures are usually caused by low gas pressure during ignition, often due to gas line sizing, too many appliances running, or low street pressure.
✅ Quick Checks
1. Power cycle
Turn the unit OFF with the front rocker switch
Wait 10 seconds
Turn ON again
👉 Listen for two clicks from the gas valve — this confirms it is trying to open.
2. Confirm other NG appliances are working
Stove burners full height?
Furnace running normally?
If these seem weak → likely low supply pressure.
3. Check Venting
Inspect intake and exhaust termination for blockages (birds, lint, snow, webs).
A partially blocked intake reduces combustion air → ignition failure.
🚫 Safety & Compliance Reminders
Use correct tools and gauge sets for gas pressure and vent static pressure measurement.
Follow all local codes and manufacturer’s installation instructions — mis-installation may void warranty.
Call a Professional
- If you smell gas, see scorch marks, or find water in the burner compartment.
- Inlet gas pressures are out of spec, pressure drop >1.5" W.C., or the unit keeps throwing 111 alongside 101/991 or 391.
Quick Links
🔍NG-Specific Causes
Here are the key things to look at. Some may be safe for you to check, others may require a licensed technician.
Undersized Gas Line
NG tankless heaters NEED:
¾" line minimum
Proper capacity depending on length & number of elbows
Undersizing leads to pressure drop exactly when the unit tries to ramp up → Code 111.
Other Appliances Drawing Gas
If furnace + dryer + heater run together → startup pressure may dip below required levels.
Street pressure issue (common in cold weather)
-
Low municipal supply causes:
Weak burner ignition
Intermittent 111 during peak demand
A tech can check this at the meter.
🔍Technician Steps
Measure Inlet Gas Pressure
Required static inlet pressure:
4.0–10.5 in. W.C. (NG)
If it dips below 3.5" during ignition → guaranteed 111.
Check Manifold Pressure
Should be ~ 2.0–2.5 in. W.C. while burning
If too low → clogged orifice or failing valve.
High-limit switch / Overheat Cutoff Fuse (OHCF) check
The manual outlines a quick electrical check if valves don’t “clunk” on reboot.
Clean flame sensor & ignition rod
Remove flame rod
Lightly sand with 100–120 grit
Replace gasket
Dirty rods = false “no flame detected.”
Check Spark Ignition Electrode
Weak spark → failed light-off → 111.