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 DC DSI / Direct Spark With 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 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 and closes the gas valve to prevent continued release of unburned propane.
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 can prevent board startup • Check furnace fuse • Check wall thermostat signal • Check wiring harness connections at the board Blower starts, pre-purge occurs, but no spark: • Verify electrode and high-voltage wire are intact and connected • Inspect electrode tip for carbon buildup or damage • Check electrode gap • 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 signal during ignition attempt • If gas valve is 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 • Check sail switch for intermittent operation • If electrode is clean and connections are good → board flame-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 manufacturers 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: 8500-I, 8500-II, 8500-III, 8500-IV 16K, 20K, 25K, 31K, and 35K BTU variants across applicable 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, use the included NBK 11455-1 adapter, equivalent to Atwood 35325. The adapter bridges the 6-pin connector on the replacement board to the 6-position edge connector on the older furnace 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, use the included adapter. If the furnace uses individual pin-type connectors, the NBK 11455 connects directly and the adapter is not required for installation. Installing the board on an edge-connector furnace without using the included adapter will result in the board not functioning. Inspect your harness connector type before installation.
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. Low battery voltage may prevent the board from initiating the ignition sequence, generating sufficient spark voltage, or operating consistently. If a furnace begins behaving erratically, check battery voltage under load before assuming board failure.
Power down before servicing: Turn the furnace off at the wall thermostat and disconnect the furnace from 12V power before removing or installing the board. Photograph the wiring before disconnecting: Take clear photos of all wiring connections before removing the original board as a reference for reinstallation. Note connector type before installation: Verify whether the furnace harness uses individual pin connectors or a 6-position edge connector. If it uses the older edge-connector style, install the NBK 11455-1 adapter included with this kit. Board fuse: If the original board appears completely dead, check its fuse before replacing the board. 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 → pre-purge → spark and gas → flame confirmation → steady heating.
"Furnace clicks but doesn't light" – Check propane supply, gas valve operation, burner orifice, electrode, and spark gap. "Furnace tries to light, then shuts off and won't try again" – Lockout mode. Flame sense may be failing. Clean and inspect the electrode first. "Furnace won't start at all – no blower, no nothing" – Check 12V supply, thermostat signal, board fuse, and wiring connections before condemning the board. "Blower starts but no spark" – Verify the electrode and high-voltage wire. If both are good, the board spark-output circuit may have failed. "Furnace runs but blows cold air after lighting" – Check the high-limit switch and sail switch. This is not typically a board failure.
• NBK 11455 Ignition Control Circuit Board • NBK 11455-1 Edge Connector Adapter (Atwood 35325 equivalent)
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, use the NBK 11455-1 adapter included with this kit. If the furnace uses the newer pin-style connection, the board installs directly and the adapter is not needed.
Board requires adequate 12V DC power for reliable operation. Check battery voltage under furnace load before diagnosing board failure. Cold weather and aged batteries can reduce available voltage and 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 can mimic a failed board in the early stages of diagnosis. High Limit Switch (Atwood 37022): A tripped or failed limit switch can cause the furnace to shut down heat unexpectedly. Gas Valve (Atwood 31099): If spark is confirmed but gas doesn't flow, check the valve and verify that it receives the proper electrical signal. NBK 11455-1 Adapter (Atwood 35325 equivalent): Required for furnaces using the older 6-position edge connector and included with the NBK 11455 kit.
• Disconnect 12V power before servicing – Remove the furnace fuse or disconnect battery power before working on furnace wiring or board connections • Do not bypass safety features – Do not jumper the sail switch, high-limit switch, or flame-sense circuit; these safety interlocks protect against dangerous operating conditions • Verify propane supply is off during board replacement – Turn off propane at the tank before opening the furnace control compartment • Check harness connector type before installing – Furnaces with the older 6-position edge connector require the included NBK 11455-1 adapter; pin-connector furnaces connect directly to the board • 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 qualified RV service technician