Atwood Furnace Troubleshooting

Atwood furnace is a heating appliance widely used in recreational vehicles such as trailers for traveling or compact motor homes. They come with digital thermostats and self-diagnostic system and offer two levels of heat output. Customers may choose from different sizes according to their needs. Even though Atwood furnaces are pretty reliable when operated well and come with warranties, some owners still may face minor malfunctions from time to time. Usually it doesn’t take much time and effort to resolve the issue and restore the normal functionality without any need to seek for professional help during a trip.

Stage 1
Find a power supply and connect the Atwood furnace to it if you notice any malfunction. Check the fuse and replace it if necessary.
Stage 2
If the power supply works fine and the furnace produces no heat, you need set a higher temperature than your current one and set the switch to “On” or “Auto” marks to make it work.
Stage 3
If there if not enough heat or the furnace doesn’t stop working, you need to clear the ventilation area. Make sure you take away any soft thing like carpeting or drapes.
Stage 4
Switch off the device and disconnect it from power supply it if doesn’t produce the required heat. Remove the filter by opening the main panel. Use the soap or any special solution to clean it from dirt and put it away to let it completely dry. Put it back inside the furnace and try to start it one more time.
Stage 5
Contact Atwood in case you face some other complicated issues.

Atwood 8535-LD Furnace Troubleshooting

Problem Cause Solution
Pilot will not light. 1. No fuel. Check fuel supply.
2. Blocked fuel lines. Check for kinks or other blockage and replace.
3. Plugged pilot orifice. Clean with air pressure or replace. (Check for spider webs in pilot or pilot orifice.)
4. Regulator out of adjustment. Adjust regulator to 11” Water Column with furnace operating.
5. Bad pilot adjustment. Check pilot adjustment screw.
6. Regulator freezing. Insert Vè cup methyl hydrate into empty gas bottle.
7. Inoperative control valve. Replace control valve.
Pilot will not stay lit when knob has been released. 1. Loose thermocouple at control valve. Tighten thermocouple finger tight plus Va turn.
2. Dirty thermocouple connection. Clean with emery paper and replace. Clean with air pressure or replace. Check and adjust.
3. Partially plugged pilot orifice. Check for millivolt out-put and replace if faulty. MIN. 5 MV closed circuit, 13 MV open circuit.
4. Bad adjustment at pilot and/or regulator.
5. Faulty thermocouple.
6. Faulty valve.
Main burner will not fire. 1. Dirty orifice. Clean with air pressure or replace.
2. Regulator freezing. Insert V2 cup methylhydrate into empty gas bottle. NOTE: If bottle is full, insert a few drops of methylhydrate into line at P.O.L. fitting.
Main burner will not fire. 1. Pilot knob not at ON position. Turn pilot knob to ON position.
2. Toggle switch OFF. Turn toggle switch to ON position. Check voltage at valve. ‘
3. Manual reset limit switch open. Push to reset limit (right side of blower housing). Check voltage at valve. Replace if continuity test shows faulty. Check voltage at valve.
4. High limit switch faulty. Replace control.
5. Inoperative control valve with 12 VDC at valve. Replace thermostat.
6. Bad thermostat. Reset and/or replace.
7. Circuit breaker out and/or faulty. Push to reset.
8. Manual reset out. Replace wire.
9. Broken wire to thermostat. Check connections to make sure they are tight.
10. Poor connection in wiring harness.

Atwood AFMD35 Furnace Troubleshooting

Problem / Cause Solution
Furnace will not light – Blower does not turn on. 1. Check the main fuse panel for a blown fuse.
2. The Furnace-installed breaker switch may be tripped or OFF – Contact a trained RV service provider.
3. The 12 VDC power is low; check the RV system voltage.
4. The Furnace may be in lockout. Reset the Furnace by switching the thermostat to OFF for 10 seconds, then switch the thermostat to ON. If air is in the propane line, repeat this process up to three times.
5. Check the intake and vents to make sure they are not blocked or obstructed.
Furnace will not light – Blower does turn on. 1. Air is in the propane line. Purge the air by turning on other appliances (like a cooktop) that are further downstream from the propane tanks.
2. The thermostat is not set to Heat or a high enough temperature. Adjust the thermostat.
Furnace shuts off before it reaches the desired temperature. 1. Check to make sure all the vents are open and not covered.
2. Check the air intake to make sure it is not blocked or obstructed.

Atwood 9525-LD Furnace Troubleshooting

Problem Solution
Thermostat Is Calling For Heat, but The Blower Does Not Run: 1. Check for 12 volts DC at the furnace connection. Correct power source if “0” volts or below 12 volts DC.
2. Check all wiring for correct polarity, loose connections and possible shorts.
3. Check the wall thermostat and wiring for continuity. Be sure thermostat points are contacting.
4. With thermostat points closed, check for circuit completion across terminals 2 and 4 of the thermostat relay. If no continuity, and wiring to the relay is okay, replace the relay.
5. If there is continuity across terminals 2 and 4, and the wiring to the motor is okay, replace the motor.
6. On time delay relay models, allow 3 to 10 seconds for the circuit to be completed to the motor, as the coil in the time delay relay must heat up to close the contacts
Blower Is Noisy: 1. Check for lint accumulation or debris on the blower wheels or possible damage to the wheel.
2. Check for excessive voltage and correct, if present.
3. Check polarity. If reversed, the motor will whine and run backward. Air delivery will be too low to close the microswitch.
4. Wheel may be hitting the housing. Remove the combustion air housing and adjust the wheel with a T-handle 1/8″ Allen wrench. On the room air wheel side, a 90* angle 1/811 Allen wrench will be needed to remove or adjust the wheel.
5. At times, insects such as mud daubers and wasps will build nests inside the combustion air housing, coming in from the fresh air intake. Remove any foreign materials and check the combustion air wheel for warpage.
6. If the bushings of the motor are worn and noise persists, replace the motor. Check both wheels for balance and, if not proper, replace the wheel or wheels
Blower Runs but Burner Does Not Light: 1. Make sure the manual shut-off valve is in the “ON” position.
2. Possible air in the gas lines. Reset the thermostat and cycle the furnace several times to bleed the system.
3. Check the gas supply. Be certain 11″ WC pressure is present while the furnace is operating. If not, adjust the pressure regulator.
4. Check the wiring for proper polarity.
5. Check for proper clearances down the sides and across the top for return air to feed the room air blower. Each model furnace has a minimum requirement of return air outlined in the installation manual. With improper return air, the air volume may not actuate the sail switch that sends voltage to the module board. All models must have I” clearance along the sides and across the top except the NT-34, -42 and -45 models, which require 2″ on the sides and top.
6. Check the ducting of the furnace to determine proper airflow away from the furnace. If the ducts have severe bends or kinks in the hose, the airflow may be restricted enough to cause the microswitch to bounce back from the volume of air hitting the cabinet front. This again will not allow voltage to the module board. Many times, a furnace will operate satisfactorily on the bench or without the door on the unit. Check for microswitch energizing when this happens. Correct ducting for proper airflow and/or replace the microswitch (could be stiff).
7. If the furnace will ignite with the cabinet front off, but will not with the cabinet front secured, and the ducting is free, check the gaskets around the burner access door. If he burner access is not properly sealed, air may be deflected from the cabinet front into the burner area, thus disturbing air and gas mixture for proper ignition.
8. Check for 12 volts DC on both sides of the limit switch. If there is voltage on one side of the switch, but not on the other, replace the switch. If voltage is present on both sides of the switch, proceed to Step 9.
9. Check for 12 volts DC at the power terminals on the module board. If no voltage, check wiring from the limit switch. Correct wiring.
10. If sparking is audible approximately 15 seconds after the blower starts, but no ignition, check the high-tension wire for continuity, grounding and secure connections. Repair if necessary.
11. Make sure electrode is not grounding to burner, the gap between the spark probe and the ground probe is 1/8″, and the ceramic insulator is not cracked, broken or sooted. Adjust, clean or replace as necessary.
12. If sparking is not audible, check the module board and observe if the neon bulb on the circuit board is flashing during the trial for ignition. Remove the white plastic wire connector from the circuit board. Clean the board terminals on back with a soft rubber eraser. Check the little pin terminals in the plastic connector for good contact. Reinstall connector. If the tube does not flash, replace the module board.
13. Check for voltage at the gas valve during the trial for ignition. If no voltage and connections are okay, replace the board.
14. If the valve does not open with 12 volts DC present, replace the valve.
15. If the electrode sparks and the valve opens but the burner will not light, check the gas supply for 11″ WC pressure to the main burner office. If 11″ is present to the valve but not to the orifice, replace the valve. Check vent and air intake installation. Check the main burner for correct relationship to the electrode assembly (burner should be 3/16″ from the spark probe and sawports or charge ports directly under the spark gap). Check main burner for soot build-up in ports. Clean cast-iron burners by passing a hacksaw blade through the sawports, being careful not to enlarge the openings. Wire brush stainless tube burners to remove build-up.
16. Check the combustion air wheel for proper rotation. Insufficient air will not sustain the flame if the wheel is installed backward
Burner Ignites But Shuts Off: 1. Check to be certain that flame sensor is over slots in the main burner and that the main burner flame is burning against the tip of the flame sensor – adjust by bending the sensor probe. NOTE: Sensor probe should be in the inner blue cone of the burner flame, approximately 1/4″ to 5/16″ above the burner.
2. If the burner still goes off and into lockout, check the wire connections at the flame sensor and the module board.
3. If wire connections are okay, check for continuity through the flame sensor wire.
4. If the continuity of the flame sensor wire is okay, check with microamp meter in series with the flame sensor and flame sensor wire to be certain the flame sensor is generating at least seven microamps within seven seconds after the burner is ignited. Connect the meter as follows: (+) to sensor wire, (-) to sensor probe. Adjust the position of the sensor probe, check air adjustment and check for carbon deposits on the sensor probe if the reading is less than seven microamps.
5. When the flame sensor circuit is generating at least seven microamps, but the burner
still goes off and into lockout, replace the module board
Main Burner Will Not Shut Off: 1. Make sure the thermostat and contact points are open.
2. Check voltage at the valve terminals – should be “0” voltage.
3. Disconnect leads from the valve. If it does not shut off, replace the valve.
Continuous Sparking Of the Electrode: 1. Check the sensor wire and high-tension wire for good connections. Check for separations in either wire – repair or replace. Check to be certain that the flame sensor probe is over the slots in the main burner and that the main burner flame is burning against the tip of the sensor probe. Adjust by bending the probe or repositioning the burner. The burner flame should be a hard blue flame, lying down on the burner
Erratic Blower and/or Thermostat Operation: 1. Check the wiring to the furnace.
2. Check for shorts in wiring.
3. Disconnect leads to the gas valve. If the furnace runs properly with the leads removed, replace the gas valve.
4. If the fan continues to run after the thermostat is satisfied and the burner goes off, the fan switch or the time delay relay is defective and needs to be replace. If the fan comes back on after a short period of time (within one minute) and cuts off and on, replace the fan switch.
5. If the thermostat is not satisfied (points still made) and the fan cuts on and off, replace the motor (thermal overload switch is defective.)
Unit Going Into Lockout Only Once In A While: 1. Thoroughly check the electrode and burner air adjustments.
2. Lockout can occur if the gas pressure fluctuates at the time that the thermostat calls for heat. Pressure fluctuations can be caused by a malfunctioning gas bottle regulator, and obstruction or a kink in the gas line, or moisture in the gas bottle regulator or in the gas lines. It is difficult to check for these fluctuations that will not noticeably affect any other appliance in the coach. However, isolating the furnace from the coach gas system will determine if the gas system is responsible. This isolation procedure can be done by connecting a separate upright bottle, regulator and gas line directly to the furnace, eliminating the coach gas system. If the occasional lockout still exists, then the furnace should be thoroughly tested to determine the cause; however, if the furnace works properly on this separate system, then the coach gas system should be checked.
3. Check the furnace return air and warm air discharge to be certain sufficient airflow is present to engage the microswitch every time.
4. Check the microswitch to be sure it moves freely.
5. Remove the electrode and burner and clean them thoroughly

Atwood 1522-LD Furnace Troubleshooting

Problem Solution
Low battery voltage The furnace is designed to operate at voltages between 10.5 to 13.5 VDC. Low voltage will not run the blower motor at the proper speed to commence the ignition sequence
Obstructed return air intake Return air is the air that flows in to replace the heated air that the blower pushes out through the ducting. This air is pulled in by the furnace through louvered openings in the side of the furnace cabinet, and any items stored near these openings could interfere with this air flow
Obstructed exhaust The exhaust venting must be clear of all obstructions for proper furnace operation. Inspect the vents for insect or bird nests or other debris
Steady on, no tlashinq Internal Circuit Board Failure
1 flash with 3-second pause Limit switch/Airflow problems
2 flashes with 3-second pause Flame Sense Fault
3 flashes with 3-second pause Ignition Lockout Fault

Atwood HYDRO FLAME AFS Furnace Troubleshooting

Problem Cause Solution
Burner fails to ignite and blower fails to run No electrical power to the furnace Reconnect or replace power source.
Current overload protector device Reset circuit breaker. Check amp draw from motor defective or tripped (circuit breaker).according to furnace’s specifications.
Thermostat defective Replace thermostat.
Thermostat wires broken Replace wire or wires.
Thermostat located in high area Relocate thermostat.
Blower motor defective Replace motor.
Blower relay defective Replace relay.
Wire off motor Reconnect wire.
Wire off relay
Furnace grounding wires not secure Clean and secure grounds established
Gas valve defective Replace valve or valve coil, depending on problem encountered.
Gas pressure incorrect Set pressure to a minimum of 11″ W.C. with all appliances running. (Replace regulator if not obtainable).
Limit switch defective or wire off Reconnect wire or replace.
Sail switch defective or wire off
Burner orifice blocked Clean main burner orifice or replace.
Combustion air wheel loose Reposition and tighten.
Exhaust blocked Clean exhaust.
Air intake restricted Clean air intake
Broken or loose wire Replace or tighten
Motor running slow Check voltage first. If 12 VDC while running, replace motor.*
Pilot orifice plugged Clean or replace orifice
Thermocouple defective Replace thermocouple
Pilot assembly defective Replace pilot assembly
Burner cycling on and off – blower runs continuously with thermostat “on” Restricted return air supply Make sure return air meets furnace’s minimum requirements.
Restricted discharge duct system a. Make sure ducting meets furnace’s minimum requirements.*
b. Make sure there is no excess ducting or unnecessary bends.*
c. Make sure any closeable registers are fully open and unrestricted.
Defective limit switch Replace limit switch.
Furnace over fired Set gas pressure to a minimum of 11″ WC with all appliances running. Replace regulator if not obtainable. Also, check main burner orifice, it must comply with furnace’s specifications.
Blower vibrates or is noisy Damaged blower wheel Replace blower wheel.
Motor shaft bent Replace motor
Loose motor Tighten motor mounting bracket.
Restricted discharge duct system requirements. a. Make sure ducting meets furnace’s minimum
b. Make sure there is no excess ducting or unnecessary bends.
c. Make sure any closable registers are fully open and unrestricted.
Electrode out of adjustment Adjust electrode to furnace’s specifications.
Pilot tube defective Replace tube.
Piezo sparker defective Replace sparker
Defective thermocouple Replace thermocouple.
Defective valve Replace valve.
Vent kit not sealed Seal vent where it meets with the furnace.
MICA window missing Replace MICA
Combustion air hose plugged or collapsed Replace combustion hose
Water in propane Add alcohol to the propane bottles.
Burner plate gasket or pilot gasket not sealed Replace gaskets

Atwood HYDRO FLAME 8935 Furnace Troubleshooting

Condition Solution
Temperature selector out of place Re-set to desired position
Thermostat wires broken or disconnected Repair wires
Heat anticipator burned out Dead short
Repair short then replace thermostat
Faulty relay drawing more than l amp
Replace relay and thermostat
No continuity through thermostat with contacts closed and switched on Replace thermostat
Continuity through thermostat with contacts closed and switched on Re-set to desired position
Thermostat wires broken or disconnected Check and re-establish power to
Reset tripped circuit breaker
Correct poor ground
Correct any loose wires
Replace defective relay
Replace defective motor
Furnace cycles too quickly Move anticipator to a higher amp setting to
lengthen cycle
High temperature variance Move anticipator to a lower amp setting to shorten cycle