In a direct spark ignition furnace, there is no standing pilot flame. Every heating cycle begins cold – and the ignition control board is responsible for managing every step of the process safely and in the correct sequence. When the thermostat calls for heat, it doesn't go directly to the gas valve; it goes to the control board, which then executes a precise, timed ignition sequence with built-in safety checks at each stage.12V DCDSI / Direct SparkWith Fan Control
The NBK 11455 performs all of these functions as a direct replacement for the Atwood 31501, restoring the furnace to full operation when the original board has failed. Because board failures can present in multiple ways – no response at all, partial ignition attempts, or a furnace that cycles but doesn't stay lit – understanding what the board does at each stage helps diagnose whether the board is actually the problem before ordering.
Powered by RV house battery / converter
Safe startup – clears unburned gas before spark
Confirms combustion before steady heating begins
Shuts down safely if ignition sequence fails
Understanding the sequence the 31501/NBK 11455 board controls explains both normal furnace behavior and how to interpret fault conditions when something goes wrong.
About the 15-Second Delay: One of the most common customer service calls about Atwood furnaces is "why does it wait before igniting?" The 15-second pre-purge is not a malfunction – it is a deliberate safety feature. The blower must run long enough to completely displace any residual propane from the combustion chamber before a spark is generated. Attempting to ignite with residual gas present could cause a hard light or mini-explosion in the combustion chamber. The delay is the board protecting the furnace and the occupants.
After gas and spark are both present, the board doesn't simply assume the burner has lit – it verifies combustion through micro-amp sensing. The igniter electrode serves a dual role: it generates the spark for ignition and also acts as a flame sensor. When a flame is present around the electrode tip, it ionizes the surrounding gas, creating a small but measurable electrical current (in the micro-amp range) that flows through the electrode back to the board.
If the board detects this micro-amp signal at or above the minimum threshold, it confirms combustion and transitions to steady heating. If the signal is absent or below threshold after the trial-for-ignition period, the board enters lockout – closing the gas valve, shutting down the blower, and stopping all further ignition attempts until the thermostat is cycled off and back on. This lockout prevents the furnace from pumping unburned propane into the combustion area in repeated failed ignition attempts.
Common cause of flame sense failure: Carbon or oxidation buildup on the electrode tip reduces its conductivity and weakens the micro-amp signal. A furnace that lights briefly then shuts off on lockout is often an electrode problem, not a board problem. Always inspect and clean the electrode tip before replacing the board.
The 31501/NBK 11455 board is the right replacement when other components have been ruled out. Before replacing the board, verify: No response at all (furnace completely dead): • Check 12V supply to board – low battery voltage (below ~10.5V) will prevent board startup • Check furnace fuse (typically 3A or 5A on the board itself) • Check wall thermostat is sending correct voltage signal • Check wiring harness connections at the board Blower starts, pre-purge occurs, but no spark: • Board generates spark signal – verify electrode and high-voltage wire are intact and connected • Inspect electrode tip for carbon buildup or damage • Check electrode gap (typically 1/8") • If electrode and wire are good and no spark occurs → board may be at fault Spark occurs, gas smell present, but no ignition: • Check propane supply – tank level, valve open, regulator function • Check gas valve – board may not be opening it (verify 12V signal at valve during ignition attempt) • If gas valve is receiving signal and opening but burner doesn't light → gas orifice may be blocked Ignites briefly then locks out: • Classic flame sense failure – clean electrode tip first • Check for drafts or airflow problems that could blow out the flame • Check sail switch – if it's intermittent, it can cause mid-cycle shutdowns • If electrode is clean and connections are good → board micro-amp sense circuit may have failed Board confirmed faulty → NBK 11455 is the correct replacement
The NBK 11455 is compatible with a wide range of Atwood Hydroflame DSI furnace series spanning multiple decades of production. These furnaces are found in RVs, travel trailers, fifth wheels, and motorhomes produced by virtually every major manufacturer that used Atwood heating equipment.
79 / 80 Series: 7912-II, 7916-II, 7920-II, 8012-II, FA7912D, FA7916D, FA7920D, HF8012D, FA79D, HF80D DC82 Series: DC8225, DC8232, DC8235, DC8241, DC82 25-32, DC82 35-41 FA / FA7 Series: FA76D, FA7615D, FA7825, FA7832, FA72D, FA72, FA78 25-32 85 Series (all BTU variants): 8500-I, 8500-II, 8500-III, 8500-IV (16K, 20K, 25K, 31K, 35K BTU variants across all series generations) 8900 / 89 DC Series: 8900-IDC, 8900-IIDC, 8900-IIIDC, 89-I DC, 89-II DC, 89-III DC AFSD Series: AFSD12, AFSD16, AFSD20 AFMD Series: AFMD20, AFMD25, AFMD30, AFMD35 DFMD Series: DFMD20111, DFMD25111, DFMD30111, DFMD35111 DFSD Series: DFSD12111, DFSD16111, DFSD20111 Also replaces OEM board numbers: 31501, 33488, 33727, 30575, Fenwal 35-535911-113
The NBK 11455 board uses a 6-pin connector configuration. However, some older Atwood Hydroflame furnaces were built with a 6-position edge connector on the wiring harness – a flat, card-edge style plug rather than individual pin connectors. If your existing furnace harness has this style of connection, you will need to purchase the NBK 11455-1 adapter (equivalent to Atwood 35325) in addition to the board. The adapter bridges the 6-pin connector on the new board to the 6-position edge connector on the older wiring harness. How to tell if you need the adapter: Look at your existing board's wiring connection. If the harness terminates in a flat, multi-finger card-edge connector (similar to a PC expansion card slot), you need the adapter. If it uses individual pin-type connectors, the NBK 11455 connects directly without an adapter. Installing the board without the correct adapter on an edge-connector harness will result in the board not functioning. Inspect your harness connector type before ordering.
The NBK 11455 operates on 12V DC – powered from the RV's house battery bank through the converter when on shore power, or directly from the battery when dry camping. This means the furnace is functional even without shore power, but battery voltage health directly affects board performance.
Low voltage caution: The ignition board requires adequate 12V supply to function correctly. When battery voltage drops below approximately 10.5V, the board may fail to initiate ignition sequences, generate insufficient spark voltage, or produce intermittent operation. If a furnace that previously worked correctly begins behaving erratically in cold weather – when battery capacity is naturally reduced – check battery voltage under load before assuming board failure. Many apparent board failures are actually undervoltage symptoms.
Power down before servicing: Turn the furnace off at the wall thermostat and disconnect the furnace from 12V power (remove the fuse or disconnect the battery) before removing or installing the board. Photograph the wiring before disconnecting: The board has multiple connectors. Take clear photos of all wiring connections before removing the original board as a reference for reinstallation. Note connector types before ordering: Verify whether your harness uses individual pin connectors or a 6-position edge connector. Order the NBK 11455-1 adapter if needed before starting the job. Board fuse: The 31501 board has an onboard fuse (typically 3A). If the original board appears completely dead and passes no power at all, check this fuse first – a blown board fuse is sometimes the only failure, not the board itself. Board dimensions: 3.88" × 6.13" × 3.88" – verify clearance in the furnace control compartment before installation. Post-installation test: After installation, cycle the thermostat on and observe the full ignition sequence: blower start → sail switch click → 15-second pre-purge → spark and gas → flame confirmation → steady heating. Each step should occur in sequence without abnormal delay.
"Furnace clicks but doesn't light" – Spark is occurring (board is generating it) but flame isn't starting. Check propane supply, gas valve operation, and burner orifice for blockage. Also verify spark gap at electrode. "Furnace tries to light, then shuts off and won't try again" – Lockout mode. Flame sense is failing. Clean electrode tip first. If that doesn't resolve it, check for drafts at the furnace combustion air intake. If both are fine, board flame sense circuit may be the issue. "Furnace won't start at all – no blower, no nothing" – Check 12V supply voltage first. Check thermostat wire connection at board. Check board fuse. If all good and board still dead → board failure likely. "Blower starts but no spark" – Board is alive and sequencing, but spark output has failed. Verify electrode wire connection. Inspect electrode for damage. If electrode and wire check out → board spark output circuit may have failed. "Furnace runs but blows cold air after lighting" – High limit switch or sail switch issue; board is shutting down heat due to a safety switch trip. Not typically a board failure.
The single most important installation step is verifying whether your furnace wiring harness uses individual pin connectors or a 6-position flat edge connector. If your harness has a flat edge connector, order the NBK 11455-1 adapter at the same time as the board. Attempting to install without the correct adapter will result in the board not functioning.
Board requires minimum ~10.5V DC for reliable operation. Check battery voltage under furnace load before diagnosing board failure. Cold weather and aged batteries produce lower available voltage that can cause intermittent or failed ignition sequences that mimic board failure.
Igniter Electrode (NBK 20284 / Atwood 35100): The electrode is the first thing to check when flame sense fails. Carbon buildup or a damaged tip are far more common than board failure for ignition/lockout issues. Sail Switch (Atwood 36680): If the blower runs but the board never advances to spark, the sail switch may not be closing. A faulty sail switch mimics a dead board in the early stages of diagnosis. High Limit Switch (Atwood 37022): A tripped or failed limit switch causes the furnace to shut down heat unexpectedly. Not a board issue, but worth inspecting if the board has been recently replaced and heating is still intermittent. Gas Valve (Atwood 31099): If spark is confirmed but gas doesn't flow, check the valve. The board sends an electrical signal to the valve – if the valve itself has failed, the board can't override it. NBK 11455-1 Adapter (Atwood 35325): Required if your harness uses a 6-position edge connector. Must be ordered separately.
• Disconnect 12V power before servicing – Remove the furnace fuse or disconnect battery before working on any furnace wiring or board connections • Do not bypass safety features – Do not attempt to jumper the sail switch, high limit switch, or flame sense circuit to "test" whether the board is working; these safety interlocks protect against dangerous conditions • Verify propane supply is off during board replacement – Turn off the propane supply at the tank before opening the furnace control compartment • Check harness connector type before installing – Installing without the required edge connector adapter on older harness styles will result in no-function; the adapter must be purchased separately if needed • Aftermarket product – This is an NBK aftermarket replacement, not an Atwood/Dometic OEM part; it is not manufactured by or affiliated with Atwood Mobile Products or Dometic • If in doubt, consult a qualified RV technician – Furnace repair involves propane gas lines, high-voltage spark circuitry, and combustion systems; if you are not comfortable with the diagnostic and replacement process, have the work performed by a certified RV service technician