Replace an Ignition Control Module (DSI / Intermittent Spark)

Replace an older direct-spark (DSI) or intermittent-pilot ignition module (distinct from the integrated IFC board): match the OEM module + ignition sequence, transfer wiring, set the spark/electrode gap, then verify flame rectification (microamp sense), trial-for-ignition timing, and that it locks out and re-tries correctly on a failed light.

Approx. 60 min

Before you start

•Confirmed the module is the fault — no spark / no gas-valve energize on a call, intermittent ignition, or a module that won't prove flame even with a clean, gapped sensor. Rule out the igniter/electrode, flame sensor, gas valve, and grounding first.
•This is the standalone ignition module (e.g. Honeywell S8600/S8610, Fenwal, White-Rodgers 50-series), NOT the integrated furnace control board — replacing an IFC is a different procedure.
•Correct OEM/cross-referenced module: same ignition system type (DSI vs intermittent pilot), same trial-for-ignition time, same flame-fail response, prepurge, and connector layout/voltage.

Tools & materials

Multimeter (microamp/DC for flame sense, ohms for ground) · Feeler gauge / spark-gap gauge · Nut drivers + screwdrivers, anti-oxidant on the ground · Phone camera + labels for the existing wiring · Replacement OEM ignition module

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Isolate & document

Kill power and verify the module type/timing
Cut and verify power. Read the old module's part number and ignition spec (trial-for-ignition seconds, lockout/retry behavior, prepurge) so the replacement matches — a wrong sequence can over- or under-purge or fail to lock out.
⚠ Lockout/tagout and verify 0 V before disconnecting the module.
Photograph and label the wiring
Photo and label every connection: 24V in, gas-valve out, igniter/spark lead, flame-sense lead, and the ground. The high-voltage spark lead and the flame-sense lead are easy to swap — note exactly where each lands.
Target: Spark lead, flame-sense lead, valve, 24V, and ground all labeled to terminal

Mount the new module & set the gap

Mount the module and land the wiring
Fasten the new OEM module and transfer the wiring per your photos. A solid earth ground is essential — the module proves flame through it; a poor ground mimics a 'no flame' fault. Clean the ground connection.
Tools: Nut drivers + screwdrivers, Anti-oxidant
Target: Solid, clean chassis ground; wiring landed exactly per the old module
Set the spark/electrode gap
Set the spark electrode (and pilot/sensor gap on intermittent-pilot systems) to the maker's gap with a feeler/gap gauge. Too wide and it won't jump a reliable spark; too tight and it weakens the flame envelope over the sensor.
Tools: Feeler gauge / spark-gap gauge
Target: Spark/electrode gap to the maker's spec (commonly ~1/8 in / ~0.10–0.15 in — verify nameplate)

Prove ignition, sense & lockout

Verify flame rectification (microamp sense)
Restore power, call for heat, and read the flame-rectification current in microamps DC in series with the sense lead. A weak signal means a dirty/misplaced sensor, a poor ground, or a small flame — fix it before trusting the new module.
Tools: Multimeter (microamp DC)
Target: Flame-sense current above the module's drop-out, commonly ≥ 1–2 µA DC (verify the module's minimum)
Confirm trial-for-ignition and lockout/retry
Watch the sequence: prepurge (if any), spark, gas-valve energize, flame proven within the trial-for-ignition window. Then simulate a failed light (block/shut the pilot or pull the sense lead) and confirm it drops the valve, retries the maker's number of times, then locks out — not endless sparking on raw gas.
Target: Lights within the trial-for-ignition time; on flame fail it closes the valve, retries per spec, then locks out
⚠ A module that keeps sparking with the valve open on a failed light is unsafe — it must lock out.