When the gas heat on a York ZF 3 to 6 ton rooftop (J03ZF, J04ZF, J05ZF) won't light, read the ignition control board (ICB) LED first. York installation manual 697890-YIM-C-0213 lists 2 flashes for the draft motor's centrifugal switch open, 3 for that switch closed with the motor off, 5 for a lockout on too many pilot flame losses, and 6 to 10 for limits, rollout, false flame, gas valve and flame sense faults. Each code points to one device to check.
How is the gas heat supposed to start?
Knowing the normal sequence tells you where it stopped. York describes it this way for the ZF036–072 (697890-YIM-C-0213):
- On a W1 call, the unit control board (UCB) energizes relay RW1, which powers the ICB.
- The ICB checks the flame sense circuit, rollout switch, centrifugal switch and the primary/auxiliary limit circuit. If all are in the right state, it starts the draft motor and waits for the centrifugal switch on that motor to close.
- The heat exchanger purges for 15 seconds.
- The ICB opens the pilot valve and fires the igniter together. The igniter stops once the flame sensor proves the pilot.
- With a stable pilot, the ICB opens the main gas valve.
- The UCB starts the indoor blower 45 seconds after the call for heat.
- When the call ends, both valves close and the draft motor runs a 30-second post-purge.
On 2-stage units, a W1-only call runs high fire for 1 minute and then drops to low fire. A W2 call during low fire switches straight to high fire.
What do the ignition control board flash codes mean?
| ICB flashes | Meaning (697890-YIM-C-0213, Table 30) |
|---|---|
| Heartbeat | Normal operation |
| 2 | Pressure or centrifugal switch open with the inducer on |
| 3 | Pressure or centrifugal switch closed with the inducer off |
| 5 | Lockout from too many flame losses |
| 6 | High temperature switch open (primary or auxiliary) |
| 7 | Rollout switch open |
| 8 | Flame present with gas off |
| 9 | Gas valve stuck off or on |
| 10 | Flame sense circuit failure |
The unit control board shows 9 flashes when the ignition control is locked out, failed or tripped on its limit, so a 9 on the UCB means "go look at the ICB". For the unit control board's own codes, see York Simplicity Lite control board flash codes. Codes 6 and 7 (limits and rollout) have their own checks, covered in York ZF rollout switch and limit trips.
What does York say to check for codes 2 and 3?
The centrifugal switch is part of the draft motor. York gives it as closing at about 2500 rpm and opening at about 2000 rpm.
- Code 2 (switch open, draft motor on): with power off, spin the draft motor wheel by hand. Clear any debris; if it still binds, replace the draft motor. With power on and a heat call, measure voltage across the draft motor leads. York says under 177 volts means repair the power circuit. Above 176 volts with the motor not turning, check the windings for an open. If the motor turns, check the switch wiring between the ICB and the motor before York's harness test, which is done with the gas valve off.
- Code 3 (switch closed, draft motor off): disconnect the 9-pin ICB connector and check continuity across harness terminals 3 and 8. Closed with good wiring means replace the draft motor. Open means reconnect, remove power for at least 20 seconds, restore it, and replace the ICB if code 3 returns.
What causes code 5, a pilot flame lockout?
York says more than 16 flame losses during one call for heat causes a 5-minute lockout. If the call is still there afterward, the ignition sequence tries again. The listed causes are:
- Low inlet gas pressure
- Debris around the flame sensor
- A plugged pilot burner
- Soot on the flame sensor
- Incorrect pilot pressure
York's check: remove power for 20 seconds, restore it, call for heat and watch the pilot flame. With a strong, stable flame, confirm the sensor position and clean or replace the sensor. With a weak flame, confirm inlet pressure is above the data label minimum and adjust pilot pressure. If that fails, pull the burner assembly, check that the pilot burner is open and clean, and check the pilot orifice size against the data plate.
Our practical advice: a sensor that looks clean can still be the problem. Check gas pressure and pilot flame before you replace the ICB.
What do codes 8, 9 and 10 mean?
| Code | What York says happens | What to do |
|---|---|---|
| 8 (flame with gas off) | The ICB keeps the draft motor running | With wiring correct and no heat call, check for control voltage at the gas valve. Voltage present: replace the ICB. No voltage: replace the gas valve. |
| 9 (gas valve stuck) | Pilot or main valve sensed off more than 1 second when commanded on, or on more than 1 second when commanded off; all outputs shut off in a hard lockout | The control ignores the thermostat. Recover by removing and reapplying 24VAC power, then find the cause. |
| 10 (flame sense circuit) | Internal hardware fault; hard lockout | Remove and reapply 24VAC power. If it persists, replace the board. |
Parts involved
| Component | Role in this issue | Where to find it |
|---|---|---|
| Ignition control board | Runs the sequence and shows the codes above | York S1-03109161000 Spark Ignition Control Board, UT, 24V | OEM Source 1 Part |
| Draft (venter) motor | Carries the centrifugal switch behind codes 2 and 3 | York S1-02435322000 Venter Draft Inducer Motor 1/40 HP, 3200 RPM, CW, 208/230V 1-Phase 60 Hz | OEM Source 1 Part |
| Flame sensor | Proves the pilot; code 5 cause | York S1-02530802000 Flame Sensor | OEM Source 1 Part |
| Spark igniter | Lights the pilot | York S1-02547816000 Spark Igniter, PSE-Y52 | OEM Source 1 Part |
| Pilot tube and pilot orifice | Pilot gas supply; plugged pilot is a code 5 cause | York S1-37306660000 Tube, Gas, Pilot, GV-HW | OEM Source 1 Part, York S1-02920422056 Orifice, Pilot #56 (.0465) | OEM Source 1 Part |
| Gas valve | Code 8 and 9 checks | York S1-6257916 Gas Valve, Natural Gas, 1/2 x 1/2 in. | OEM Source 1 Part, York S1-VR8204M1026 Gas Valve, Honeywell VR8204M1026, Natural Gas, 24V, 60 Hz, 1/2 x 1/2 in. | OEM Source 1 Part |
All of the parts above are listed on our J04ZF page for some or all J04ZF models. Match the number on your old part.
Which York units this applies to
- York J04ZF parts: 4-ton ZF rooftop with the ignition parts above.
- York J03ZF parts: 3-ton ZF rooftop, same ignition board listed.
- York J05ZF parts: 5-ton ZF rooftop, same ignition board listed.
- York DH060 parts: our page lists the same ICB and flame sensor for many DH060 models, but York's DH manual was not used here.
- York DM060 parts: same note as DH060; confirm by part number.
Scope: This article covers York installation manual 697890-YIM-C-0213 (ZF036 to ZF072, R-410A, 60 Hz, single- and 2-stage gas heat with proven pilot). Voltages and timings are from that manual; check your own unit's manual for 50 Hz units and other product lines.
Before you order
Write down the ICB flash code, the unit model and serial number, and the part number on the failed part. Gas valves and draft motors vary within one series, so match the old part number. To confirm fit, contact us at help@totalhvacparts.com or 610-487-7999.
Frequently Asked Questions
What does 2 flashes on a York rooftop ignition control board mean?
On the ZF036–072, York lists 2 flashes as the pressure or centrifugal switch open while the inducer is on. Check that the draft motor turns freely and has proper voltage, then check the switch wiring.
What does 5 flashes on a York ZF ignition control mean?
It is a lockout from too many flame losses. York says more than 16 flame losses on one call causes a 5-minute lockout; check inlet gas pressure, the pilot burner and the flame sensor.
How long is the purge before a York ZF rooftop tries to light?
York manual 697890-YIM-C-0213 gives a 15-second heat exchanger purge after the centrifugal switch closes, and a 30-second post-purge after the call ends.
How do I clear a 9-flash gas valve lockout on a York ZF unit?
York says the control ignores the thermostat in this hard lockout. Remove and reapply 24VAC power, then find out why the valve was sensed stuck.
Sources
- York form 697890-YIM-C-0213, Installation Manual, ZF Series R-410A, ZF036–072, 60 Hz (gas heating sequence and operation errors, page 54; ICB troubleshooting, pages 63–64; Table 30 ignition control board flash codes, page 66)
- Live product titles and series page part lists, as shown on each product page
Gas heat service involves line voltage, fuel gas and combustion products. Service should be performed only by qualified personnel, following York's manual for your unit and your facility's lockout/tagout procedures.