Table of Contents
Symbio 700 uses a communicating ignition module using Modbus to pass commands, status and diagnostics back and forth.
Before Symbio 700 will command heating on, the following criteria must be met:
- Unit must be in Heat Mode
- Supply fans must be online and communicating
- Ignition Module must be online and communicating
- No other unit lockouts present on the unit
Is my unit in Heat Mode?
Verify on the Home page of the Symbio 700 mobile app that the unit HEAT COOL MODE STATUS = HEAT
- For thermostat control units, this will show heat anytime there is a call on W1 and/or W2
- For dual fuel heat pump units, gas heat is requested on W2 or X2
- A unit with any cooling call with a heating call will show FAN ONLY and will not heat or cool
- For zone sensor controlled units, heat mode is driven by space temperature vs. space temperature setpoint. It may be necessary to raise the setpoint through the BAS or at the zone sensor to force heat mode.
- For units configured as VVDA (MZVAV), there is a 6 min time delay before the unit will begin to heat, this applies in test mode as well.
If not able to get the unit in heat, use Test Mode located in the TOOLS menu of the Symbio 700 mobile app.
Does the IGN Module have power?
The IGN Module has a status LED located on the right side of the module that gives the status of the module.
IGN LED1 will be solid green with no heat call or in a slow pulse (3/4 sec on, 1/4 sec off) for a heating call. LED1 will also blink codes (1/4/ sec on, 1/4 sec off with a 2 sec pause at the end of the code) for diagnostics. See the link below for details on LED1 blink codes:
Precedent with Symbio 700 - Ignition Controller Board Module Diagnostics
If LED1 is out, this indicates that there is no power to the ignition module. 24vac is applied to the ignition module on J8 and a 3A blade type automotive fuse protects the board from shorts:
If 24vac power is not present on IGN J8, check:
- Transformer 2 (TNS2) for a tripped breaker
- Check primary fuses and connections to TNS2 including connector on transformer primary pigtail
- Check secondary connections to TNS2 including connector PPM2/PPF2
- Check through panel connector on right side of Symbio 700 control panel, PPM72/PPF72
- Check for power on Adapter Board J8
- Check for power on Adapter Board J7
- Check connection coming from Adapter Board J7 to PPM96/PPF96
Symbio 700 Diagnostics for Ignition Module with no power
- Diagnostic: Heat Failure
- Diagnostic: Gas Heat Ignition Module 1 Communication Status
One Flash Diagnostic on LED1 (¼ sec on, 2 ¼ sec off)
No Communications
A 1 Flash diagnostic on the board is indicating that the ignition module has power but is not communicating to the Symbio 700. This indicates a problem with the Modbus between the Symbio 700 and ignition board E6 (Modbus connection). The same alarms will be present in Symbio 700 as the ignition module not being powered.
The Modbus voltage can be measured with a meter as the ignition board.
Black - Red should be between 4.8 - 4.9vdc on R410A units, 4.0 - 4.1vdc on R454B units
Black - Blue should be between 4.8 - 4.9vdc on R410A units, 4.4 - 4.6vdc on R454B units
Red - Blue should be 0 - .5 vdc on all units
If communication is not present, disconnect the Modbus to all other Modbus devices in the unit including:
- Supply Fan(s)
- Supply Fan VFD (if equipped)
- Compressor VFD (if equipped)
- A2L Leak Detection Sensor (if equipped)
If the voltage comes back after disconnecting these devices, plug them in one at a time an monitor the voltage. If one specific device takes the voltage back down, check the connections and wire for that device and verify that there are no shorts or damage to the wire.
If disconnecting other Modbus devices does not resolve the issue, begin checking the wiring for the ignition Modbus. Follow the Modbus wire back through the unit:
- Check connector MODBUS-2B
- Check the splice into the main Modbus harness to the top right of the ignition module
- Check connector MODBUS-1
- Check connector PPF116/PPM116 (right side of Symbio 700 cabinet)
- Check connector P1 on Symbio 700
If all connections checkout and voltage is still missing, disconnect P1 from Symbio 700 and check pins 1 & 2 (where the black and red wires are connected), if there is no voltage there, contact Tech Support for further assistance.
If voltage comes back with P1 disconnected, disconnect the Modbus connection from the ignition module and check the voltage on the wires again, if it comes back, this indicates the ignition board is the issue and is dragging the communications down. An issue like this would likely cause all Modbus devices in the unit to be down also.
Symbio 700 Diagnostics for 1 Flash
- Diagnostic: Heat Failure
- Diagnostic: Gas Heat Ignition Module 1 Communication Status
Two Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 2 times w/ 2 sec pause)
System Lockout: Failed to detect or sustain flame
A 2 flash diagnostic indicates that either no flame was sensed on ignition or that the flame dropped out while running. Troubleshooting for this issue would be the same for any gas heat unit that uses a flame sensing rod for proving.
- Verify that the gas is on to the unit and the inlet/line pressure to the gas valve is between 4.5" - 14"
- Verify that gas valve opened and that manifold pressures are set correctly (see unit IOM for pressures)
- Verify that spark ignitor is sparking and that there is gas flow on that burner
- Using a microamp (µA) meter, check the DC microamps at the "Flame TP" terminals on the ignition board
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- Nominal flame signal will be 4.5 µA within the 30s after the flame has been established. Flame across the sensor should register at a minimum of 1.2 µA to be considered a valid flame signal.
- For more details on test the flame sensor → Precedent with Symbio 700 - Gas Heat Flame Sensor Troubleshooting
Symbio 700 Diagnostics for 2 Flash
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Module Lockout
- Diagnostic: IGN1 No Flame Sensed on Ignition
Three Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 3 times w/ 2 sec pause)
Pressure Switch failed to close or stay closed
A 3 flash diagnostic indicates that the the pressure switch did not close in the correct amount of time after the combustion fan was energized, opened while the unit was heating or is closed when the combustion fan is commanded off.
Combustion Fan not running
The combustion fan is a 2 stage 208-230/1ph capacitor start motor. The ignition module takes 208-230vac in on J13 L1 & L2 (labeled E13 on board) and switches the L2 leg between Lo or Hi/Single to operate the fan on J12 (labeled E12 on board). J12-L1 is always hot when J13-L1 has power.
**All staged gas heat units will have 208-230 to IGN either from the main power to the unit or through a stepdown transformer on 460/575vac units.
When the combustion fan is commanded on, 208-230v can be measured on J12-L1 and J12-Hi/Single, this same voltage should be present on the combustion fan connection on
- PPM95 - ORG - BK/YL
- PPF95 - BK - R
Power present on PPM95 and missing on PPF95 indicates a faulty connector. Connector can be cut out and wires can be reconnected using insulated quick connects. Butt splices are acceptable, but will limit future serviceability of the CFM.
If a faulty connector is found, please use the red "Get Support" button above and submit a Tech Support ticket.
Do not use wire nuts or Wago style connections. These have been shown to fail in the field for various reason including corrosion and ability to maintain a secure connection.
If power is present at the motor wiring and there is no combustion fan operation, replace the combustion fan assembly.
Combustion Fan Runs, but I'm getting a still getting a 3 blink code on the ignition module
If the combustion fan is coming on, but still not making the pressure switch, verify the following:
- pressure switch tube and pickup port on heat exchanger/combustion fan housing are clear of debris and moisture
- Verify IGN J10 -5 (Y) has 24vac while combustion fan is running
- Verify the PPF105/PPM105 is connected
- Using a manometer, tee into the pressure switch line to validate the pressure the switch is seeing.
- The switch trips at 0.15" wc +/- 0.07" wc
- The switch opens ~ 0" wc
- If pressures are not high enough to actuate the switch, verify that the exhaust flue is open and not obstructed and that the burner openings are also not obstructed
Symbio 700 Diagnostics for 3 Flash and pressure switch failed to open
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Inducer Proving Switch Fail Open
No call for heat, but I'm getting a still getting a 3 blink code on the ignition module
This fault can also be caused by a pressure switch that is closed when the combustion fan is not commanded on or jumped out.
Verify that the switch is wired for Normally Open operation, closes on pressure and that there are not jumpers present across the pressure switch terminals/wires. If testing shows the switch closed with the wires removed, replace the pressure switch.
Symbio 700 Diagnostics for 3 Flash and pressure switch failed closed
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Inducer Proving Switch Fail Closed
Four Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 4 times w/ 2 sec pause)
High Limit switch protection device open
A 4 flash diagnostic indicates that one or both of the Thermal Cutout (TCO) switches are open during a call for heat. TCO lockouts are auto reset and will do not require a manual reset. When a TCO trips, it will keep the supply fan on, run the combustion fan at high speed.
TCO1 and TCO2 receive power from the ignition module when there is an active call for heat. They are wired in series where TCO1 feeds 24vac to TCO2. Trouble shooting should always start by verifying that 24 vac is present on both sides of TCO1 then down to TCO2.
The 24vac path is shown below:
TCO trips are typically caused by a low airflow situation or damaged TCO wiring/switch/mounting. TCO locations vary based on the unit size, for TCO location information see:
Thermal Cutout (TCO) Locations on Gas Heat Units with Symbio 700 Controls
Large Precedent (serial number ending in D) utilize a sensing tube to "feed" the air temp to TCO2. If this tube is damaged or bent into the heat exchanger, it can cause nuisance TCO2 trips.
For information on setting up airflow on a Precedent units, see the link below:
Setting Airflow on Precedent with Symbio 700 Controls
Symbio 700 Diagnostics for 4 Flash
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Heating High Temp Limit Open
Five Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 5 times w/ 2 sec pause)
Flame sensed and gas valve not energized, or flame sensed and no call for heat.
A 5 flash diagnostic indicates that the ignition module is sensing a flame without a call for heat. This could be a failing flame sensor or a gas valve that is not closing. When the ignition board is in a five flash, the combustion fan will be on at high speed.
Troubleshooting would include checking the signal from the flame sensor as shown in the troubleshooting for a 2 flash diagnostic shown above.
If the gas valve is not closing, immediately isolate/close the gas valve from the unit
If voltage is present remove the low voltage connection from the valve and check voltages again from the board, stray voltage from the board with no call requires ignition board replacement and locking the gas valve out until the board is replaced.
Verify wiring between the ignition board and gas valve.
If voltage is not present and the valve is staying open, lock out the gas until the valve is replaced.
Symbio 700 Diagnostics for 5 Flash
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Flame Sensed w/Gas Valve Off
Six Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 6 times w/ 2 sec pause)
Flame Rollout Switch open
A 6 flash diagnostic indicates that the temperature at the top of the heat exchanger has reached the trip limit and or there is an actual flame on the top of the burner (rollout).
The Flame Rollout (FR) receives power from the ignition module when there is an active call for heat. Trouble shooting should always start by verifying that 24 vac is present on both sides of FR.
The 24vac path is shown below:
Troubleshooting flame rollout includes:
- Check heat exchanger for cracks
- Check for dirty/stopped up heat exchanger (typically caused by improperly set gas pressure, set too high)
- Check gas pressures, see IOM for settings
- Check combustion fan operation and verify that it is running in both speeds and is staying on at all times
- If the combustion fan is shutting off and the heat is not shutting off in 5-9 seconds after the fan loses power, a functional check of the pressure switch is necessary
A tripped flame rollout requires a manual reset at the flame rollout switch.
If the switch, wiring, burner or any other part of the burner is compromised from a flame rollout, close and lockout the gas valve until repairs can be completed.
Symbio 700 Diagnostics for 6 Flash
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Flame Rollout Switch Open
Seven Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 7 times w/ 2 sec pause)
Weak Flame Sensed
A 7 flash diagnostic indicates that the flame sensor is not providing a strong enough signal to ensure to the ignition board that the flame is strong. This is typically when the flame signal is at the min value (1.2µ ) for long periods.
Troubleshooting a weak flame includes:
- Check gas pressures, see IOM for settings
- Check flame sensor for build up or corrosion
- Verify that the flame sensor rod is "bathed" in the flame in the top third of the flame with the rod covering completely from side to side
Flame sensors are all placed in the top 1/3 of the flame on the TOP burner on all models. The location of the sensor can change from left or right side depending on the unit and burner size.
A properly located flame sensor with proper gas pressures and a 7 flash code typically points to a failing or dirty flame sensor.
Symbio 700 Diagnostics for 7 Flash
- Diagnostic: IGN1 Weak Flame (warning only)
Eight Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 8 times w/ 2 sec pause)
Internal Error
A 8 flash diagnostic indicates that the ignition board has detected and/or is experiencing and error within itself. Typical causes are failing components on the ignition board, physical damage or water damage.
There is no repair option or troubleshooting for a failing/damage board, replacement is necessary.
Symbio 700 Diagnostics for 8 Flash
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Module Failure
Nine Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 9 times w/ 2 sec pause)
Gas Valve On Error
A 9 flash diagnostic indicates that the ignition board has detected the gas valve is detected ON when it should be off. The unit response is similar to a 5 flash diagnostic with the combustion fan on at high speed.
Troubleshooting is the same as a 5 flash diagnostic.
If the gas valve is not closing, immediately isolate/close the gas valve from the unit
Symbio 700 Diagnostics for 9 Flash
- Diagnostic: Heat Failure
- Diagnostic: IGN1 Gas Valve Error
Ten Flash Diagnostic on LED1 (¼ sec on, ¼ sec off, 10 times w/ 2 sec pause) ****LoNOx units only****
Low NOx Temperature Limit Lockout
A 10 flash diagnostic indicates that the Low Ambient Temp Limit Switch located in the burner section of the heater has tripped. This is a protection device for the heater which trips if the ambient temp drops below ~32°F. If tripped while actively heating, the heat will be locked out for at least and hour.
Symbio 700 Diagnostics for 10 Flash
- Diagnostic: IGN1 Low Ambient Lockout (considered a normal shutdown like no call for heat)
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.