Per York form 127408-YIM-B-0606 (Predator DM090–DM150, 50 Hz), the ignition control board will not open the gas valve until the draft (venter) motor has proven and a 30-second purge has run. If the pressure switch opens for 2 seconds during ignition, the gas valve is de-energized, ignition aborts and the control flashes a code. Three failed ignition tries or five recycles give a one-hour lockout.
That manual covers the 50 Hz DM units. The 60 Hz DH Predator technical guide (form 246646-YTG-C-0606) confirms DH units also use electronic spark ignition, power venting and flash codes on both control boards, but it does not give these timings. Treat the values below as DM090–DM150 values and confirm them against the manual for a DH unit.
What is the normal gas heat sequence on a Predator DM unit?
Form 127408-YIM-B-0606 describes the first stage of heat this way:
- The thermostat closes R to W1. The call passes through the unit control board (UCB) to the ignition control board (ICB).
- The ICB energizes the draft motor.
- Once the draft motor is proven, a 30-second purge starts.
- At the end of the purge, the gas valve opens and the spark igniter runs for 10 seconds.
- The ICB checks for flame. With flame, it enters flame stabilization. Without flame, the gas valve closes and a retry begins.
- Losing flame for 2 seconds during stabilization, or for 3/4 second after it, closes the gas valve and starts a retry.
- The UCB senses gas valve voltage, starts the heating fan-on delay and then brings on the indoor blower.
- When the thermostat is satisfied, the gas valve closes at once, the blower stops after the fan-off delay and the draft motor runs a 30-second post-purge.
On a W2 call, the ICB runs a complete first-stage ignition sequence first. If that succeeds, the second main valve opens.
What do retries, recycles and lockout mean?
| Event | What triggers it | Result |
|---|---|---|
| Retry | Flame lost or not detected during ignition | 30-second purge between attempts. After three failed attempts, one-hour lockout |
| Recycle | Flame lost after flame stabilization | After five recycles, one-hour lockout |
| Lockout | Three retries or five recycles | Cycling the low-voltage power cancels the lockout |
How does the pressure switch and venter circuit work?
The manual says the ICB monitors the pressure switch (PS). After the draft motor reaches full speed and closes the PS during ignition, a PS opening of 2 seconds de-energizes the gas valve, aborts ignition and makes the ICB flash a code. The draft motor keeps running until the PS closes or W1 is lost.
The rollout switch (ROS) is wired in series with the PS. The ICB cannot tell them apart and responds the same way to either, and an open rollout prevents the gas valve from opening. So a "pressure switch failed to close" code can also point to an open rollout switch.
Our practical advice, not from the manual: when you see a pressure switch code, check the rollout switch, the venter wheel, and the pressure switch hose and port before replacing the switch.
What do the ignition control flash codes mean?
| ICB LED | Fault condition (127408-YIM-B-0606, Table 53; same pairing in ZJ150 form 1183875-YIM-A-1014) |
|---|---|
| Steady on | Control failure |
| Heartbeat | Normal operation |
| 2 flashes | Pressure switch stuck closed |
| 3 flashes | Pressure switch failed to close |
| 4 flashes | Limit switch open |
The table also lists flame present with gas off, gas valve energized out of sequence, ignition lockout and no power or control failure. The web copy we read does not line those rows up with flash counts cleanly, so read them from the label in your control box. On the UCB, 9 flashes means ignition control locked out or ignition control failure (Table 52).
What checks does the manual give for the gas valve and flame sensing?
| Condition | Control response (127408-YIM-B-0606) |
|---|---|
| ICB senses voltage at the gas valve when none is requested | Energizes the draft motor and will not operate the furnace. The draft motor stops when no voltage is sensed at the valve |
| UCB senses gas valve voltage for 5 continuous minutes with no call for heat | Locks on the indoor blower and starts a flash code |
| UCB senses no gas valve voltage for 5 continuous minutes during a call for heat | Starts a flash code; the blower is not locked on |
| Flame sensed for 2 seconds without W1 | Draft motor runs with the gas valve off and the ICB halts operation |
| Flame detection circuit fails its self-test | Ignition is blocked and the draft motor runs; a failure during ignition counts as a recycle |
Which limits shut the burner down?
The main limit switch sits in the heater compartment and resets automatically. The auxiliary limit sits in the supply air compartment, is manual reset, and is wired in series with the main limit. If the UCB senses zero volts from the limit, it brings on the indoor blower at once. Three limit openings within one hour lock the blower on and start a flash code. The Table 46 footnote gives rollout = 300°F (148.9°C) and auxiliary limit = 200°F.
The manual clears gas heat flash codes by removing the call for heat: set the thermostat below the space temperature.
Parts involved
| Component | Role | Where to find it |
|---|---|---|
| Pressure switch | Proves the draft motor before ignition. Listed for DH090, DH078, DH102, DF090 and DM090 models. | York S1-02439479000 Pressure Switch, -0.33 in. W.C. | OEM Source 1 Part |
| Venter (draft motor) kit | Supplies combustion draft. Listed for DH090, DH078, DH102, DF090 and DM090 models. | York S1-32639532000 Venter Blower Kit with Motor and Gasket, Fasco 7062-5155 | OEM Source 1 Part |
| Gas valve | Opens at the end of the purge. Listed for DH090, DH120 and related Predator models. | York S1-02546611000 Natural Gas Valve, 24V, White-Rodgers 36H55-405 | OEM Source 1 Part |
| Spark igniter and flame rod | 10-second spark, then flame proving. | York S1-02535305000 Gas Igniter, Spark | OEM Source 1 Part and York S1-02535306000 4 in. Gas Flame Sensor (Flame Rod) | OEM Source 1 Part |
| Main limit | Auto-reset limit. Listed for DH090, DH078 and DM090; DH120 lists other limit values. | York S1-02535361000 Limit Switch, 165 Open / 135 Close, Auto Reset | OEM Source 1 Part |
| Manual-reset temperature controls | Listed for DH090 and DH120. Their title ratings (200°F and 300°F) match the manual's auxiliary limit and rollout values; confirm by part number. | York S1-02527747002 Temperature Control, 200 Open, Manual Close | OEM Source 1 Part and York S1-02535363000 Temperature Switch, 300 Open, Manual Close | OEM Source 1 Part |
| Burner | Listed for DH090, DH120 and DM090. | York S1-02922158000 Gas Burner | OEM Source 1 Part |
Which York units this applies to
- York DH090 parts — 7.5-ton Predator (60 Hz DH), the primary page for these parts. Confirm values against the DH manual.
- York DH120 parts — 10-ton Predator.
- York DF090 parts — 7.5-ton Predator.
- York DH078 parts — 6.5-ton Predator.
- York DH102 parts — 8.5-ton Predator.
- York DM090 parts — 7.5-ton Predator, the model family the cited manual covers.
Scope: The sequence, error handling, flash codes and limit values are from York form 127408-YIM-B-0606, Installation Manual for Predator DM090, DM120 and DM150 (7-1/2 to 12-1/2 ton, 50 Hz) only. We could not obtain the 60 Hz DH installation manual, and no document we read says these values apply to DH units. The DH technical guide (246646-YTG-C-0606) confirms only that DH078–DH150 gas/electric units use spark ignition, power venting and UCB/ICB flash codes. The DH090, DH120, DF090, DH078 and DH102 pages list many of the same gas heat parts, but confirm timings and settings against the manual for your unit. Part listings come from our series pages.
Before you order
Note the nameplate model and serial number and the part number on the failed component. Gas valves, venters and limits vary by heat input and generation. Contact us at help@totalhvacparts.com or 610-487-7999 to confirm fit.
Frequently Asked Questions
How long is the purge before ignition on a York Predator?
Per form 127408-YIM-B-0606 (DM090–DM150, 50 Hz), a 30-second purge starts once the draft motor is proven. The gas valve then opens and the spark runs for 10 seconds.
What does 3 flashes mean on a York Predator ignition control?
In form 127408-YIM-B-0606 (DM090–DM150), three flashes means the pressure switch failed to close. The rollout switch is wired in series with the pressure switch, so check it too.
How do you reset a York Predator gas heat lockout?
The manual says cycling the low-voltage power cancels the one-hour lockout. Flash codes clear when the call for heat is removed.
How many ignition tries does a York Predator make before lockout?
Per form 127408-YIM-B-0606 (DM090–DM150), three failed ignition attempts, with a 30-second purge between them, give a one-hour lockout. Five recycles after flame stabilization also lock out for one hour.
Sources
- York form 127408-YIM-B-0606, Installation Manual, Predator DM090, DM120, DM150 single package air conditioners and gas/electric units, 50 Hz (gas heating sequence and errors p.43, safety controls and Table 46 p.44, Table 52 UCB flash codes p.50, Table 53 ignition control flash codes p.51)
- York form 246646-YTG-C-0606, Technical Guide, Predator DH078, 090, 102, 120 and 150 high-efficiency single package A/C and gas/electric units (spark ignition, power venting, UCB and ICB flash codes)
- York form 1183875-YIM-A-1014, Installation Manual, ZJ150 (Table 30 Ignition Control Flash Codes, cross-check of codes 2 to 4)
- Part listings per series from our York S1 series pages, sourced from York's parts data
- Live product titles for the parts listed above, as shown on each product page
Gas heat service involves line voltage, natural or LP gas and combustion products. Service should be performed only by qualified personnel, following the manual for your unit and your facility's lockout/tagout procedures.