CaptiveAire DOAS RTU Series, Installation, Operation And Maintenance Manual

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Furnace Troubleshooting Chart
Problem Potential Cause Corrective Action
Furnace Does Not
Light/Stay Lit
Main gas is off Open main gas valve.
Shut off valve closed Open shut off valve.
ON/OFF gas valve is off Turn ON/OFF gas valve on.
Gas pressure out of range Adjust to proper gas pressure.
Air in gas line Purge gas line.
Dirt in burner orifices Clean orifices with compressed air.
Spark igniter rod out of position Relocate spark igniter rod to proper area.
No spark at igniter
Refer to “Flame Safety Control (FSC-01)” on page 126 .
Defective flame safety controller
Excessive drafts
Re-direct draft away from unit.
Safety device has cut power Check limits.
Check airflow switch and tubing at the MUA board.
Dirty flame sensor Clean flame sensor.
Defective flame sensor Change heating set-points to call for heat.
Defective valve Refer to “Gas Valves” on page 125 .
Loose gas valve wiring
Thermostat not calling for heat Change heating set-points to call for heat.
Unit cycling on high limit
Check gas pressure. Increase airflow through furnace, if
required.
Not Enough Heat Main gas pressure too low Increase main gas pressure – do not exceed 14 in. wc inlet
pressure.
Unit locked into low fire Check wiring or modulating valve settings. Refer to
“Furnace Start-Up Summary” on page 80 .
Too much airflow Decrease airflow if possible.
Furnace undersized Check design conditions.
Gas controls not wired properly Refer to “Gas Valves” on page 125 .
Thermostat setting too low Increase thermostat setting.
Thermostat malfunction Check thermostat.
Too Much Heat Defective modulating gas valve Check/replace modulating valve.
Thermostat setting too high
Decrease thermostat setting.
Unit locked into high fire Check modulation valve settings. Refer to “Furnace Start-
Up Summary” on page 80 .
Thermostat wired incorrectly Check thermostat wiring.
Too much primary air Reduce primary air.
Manifold pressure set too high Reduce manifold pressure.
Lifting Flames or
Flashback
Dirty orifice Check and clean orifice.
Orifice too large Check orifice size.
Insufficient primary air Increase primary air.
Yellow Tipping Flames Misaligned orifice Check manifold alignment.
Insufficient primary air Increase primary air.
Orifice too large Check orifice size.
Floating Flames or
Flame Rollout
Manifold pressure too high Decrease manifold pressure.
Blocked vent Check venting system.
Misaligned orifice Check manifold alignment.