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.
✅ 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. Check LP tank level
❗ If below 30%, vapor pressure drops noticeably.
❗ Below 20%, 111 is extremely common.
3. Check for regulator icing
LP regulators freeze when:
Cold weather
High draw
Moisture inside regulator vent
Look for frost or ice around the regulator.
4. Confirm other LP appliances work normally
If stove flames are tiny or furnace won’t run → NOT the boiler, it’s the tank/regulator.
🚫 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
🔍 LP-Specific Causes
Here are the key things to look at. Some may be safe for you to check, others may require a licensed technician.
Step 1: Two-State Regulator Issues
-
LP systems must have:
First stage at the tank
Second stage near the house
- If the second regulator is far from the tankless, ignition can fail.
Step 2: Tank too small for heater demand
-
A 199,000 BTU heater can exceed vaporization rate of small tanks, especially:
In winter
With a 100-lb cylinder
Tank cannot vaporize propane fast enough → low pressure → 111.
Step 3: Regulator Vent Blocked
Mud daubers and insects love regulator vents.
Blocked vent = erratic gas pressure.d
🔍Technician Steps
Step 4: Verify LP Inlet Pressure
Static requirement:
8.0–14.0 in. W.C. (LP)
During ignition it should remain above 8.0".
If it drops to 5–7" → ignition fails.
Step 5: Measure Manifold Pressure
For condensing models like the HS120Plus, ensure the condensate drain is open, piping is clear, and there is no blockage of the heat exchanger causing back-pressure or improper exhaust flow.
If the exchanger is restricted, the unit may struggle to draw or exhaust properly leading to improper combustion.
Step 6: Check Manifold Gas Pressure
Should be ~ 7.0–8.0 in. W.C.
If off → burner won’t fire.
Step 7: Inspect LP Regulators
Tech checks:
Lock-up pressure
Creep
Freeze/icing
Vent obstruction
Step 8: High-Limit Switch/Overheat Cutoff Fuse Check
The manual outlines a quick electrical check if valves don’t “clunk” on reboot.
Step 9: Clean Flame Sensor & Ignition Rod
LP burns “sootier,” so rods foul slightly faster.
- Remove flame rod
Lightly sand with 100–120 grit
Replace gasket
Dirty rods = false “no flame detected.”