02 Burner did not operate during freeze protection

What the control is telling you

The burner failed to fire while the unit was running its freeze-protection cycle. The checks cover gas supply, ignition, flame sensing, combustion air and venting.

Applies to: Non-SENSEI series only

Likely causes

• Gas valves closed, air in gas lines, or inlet gas pressure too low or too high
• Wrong gas type, or gas type DIP switch set incorrectly
• No spark from the igniter, or a loose, dirty or miswired electrode/flame rod
• Blocked burner orifices, debris in the burner, or clogged heat exchanger fins
• Venting problems (clearances, materials, length, DIP settings, blocked condensate trap)
• Moisture in the gas valve tube or wiring harnesses
• Faulty gas valve, PC Board or MSA/MSB staging system

Test and repair steps

1. Make sure all gas valves are open and air was purged from the gas lines. Check that the site gas type matches the rating plate and the gas type DIP switch on the PC Board.
2. Measure inlet gas pressure with every gas appliance on site at high fire. The minimum on the rating plate must be held. On condensing models, install the front panel before testing.
3. Warning: Shut off the gas valve feeding the heater before the spark test.
4. Spark test hold the unplugged igniter wire with insulated pliers 1/4 in. from metal, call for hot water. No spark: check plugs, parts and ignition board voltage (Tech Data Sheet). Voltage only appears during ignition.
5. Check that the sparker electrode and flame rod(s) cannot move by hand. If loose, clean them and refit with a new gasket. Confirm each flame rod wire matches the letter stamped on its bracket (Y/R/B).
6. Watch the view window during ignition. If flame is visible, the fault is in flame rectification: deposits, bad connection, damaged rod, PC Board, gas valve or low gas pressure. Keep going before replacing parts.
7. Warning: Turn off electrical, gas and water supply. Then remove the igniter and flame rod assemblies, clean off deposits and reinstall them. Have a new electrode packing ready in case it is damaged.
8. With power, gas and water off check manifold orifices for blockage, clear debris from the burner and air chambers, and blow out clogged fins at 120 psi. Replace the heat exchanger if it will not clean.
9. Caution: Wear safety glasses and a mask when blowing out the burner.
10. If gas pressure was wrong, check gas line sizing. Max drop at full fire: 0.3 in. W.C. natural gas, 0.5 in. W.C. propane (black iron, up to 14 in. W.C.). Have a gas sizing professional check if exceeded.
11. Check the vent for loose joints, wrong fittings, terminal clearances, approved materials, length and vent-length DIP switches. Also confirm altitude DIP switches and manifold pressures per the manual or Tech Data Sheet.
12. Indoor units moisture in the plastic tube from the combustion chamber to the gas valve means replace the gas valve and find the moisture source. Check the condensate trap/line on non-condensing units (not RH-180).
13. Two-stage regulator must be 6 ft or more away. With the heater off, static inlet pressure must stay under 10 in. W.C. (NG) or 13.5 in. (LP), else the regulator may be bad. Then cut power and check harnesses for moisture.
14. Isolate the unit from any MSA/MSB system. Other checks: electrode position, burner cassettes seated, swap the 4 burners under the flame rod with high-fire burners, then replace the gas valve or PC Board if needed.

Settings for these units

• RUCS/RUS unit clearances · Non-SENSEI
• RUCS/RUS water quality limits · Non-SENSEI