FieldBench

Lennox

SL297NV

Furnace · Signature · ultra-low emission · VS · communicating

Lennox Signature SL297NV variable-speed ultra-low emission. iComfort bus. Premix burner. Not SLP99V modulating and not EL296V 24V Elite.

Not SLP99V modulating iComfort. Not EL296V. Not EL195NE Elite ULN.

Walk this in Diagnose

This plate

NOx
Signature ultra-low emission VS
Bus
iComfort communicating

This board

iComfort IFC

  • Stat event list is primary. It names the E-code in English. Write the E-number anyway.
  • E105 = RS bus. Native here — not the ‘someone landed data wires’ story from EL296V.
  • E2xx pressure / limit / flame codes still mean the same physics as the EL296 SureLight table. The stat just names them.
  • Capacity on the display is a percent, not stage 1 / stage 2. Do not land a non-communicating stat on i+/i−.

Sequence

  1. Call. Stat requests %. Valve and inducer modulate. Blower CFM follows. There is no W1/W2 prove pair like EL296V.
  2. Prove. Inducer must hit the pressure band for that firing rate. E223-family on the stat is a band miss, not ‘swap the low PS and leave.’
  3. Ignition. Still HSI + flame rod. E207 / E240 / E270 still mean ignitor / µA / retries.

Faults on this IFC

  • E105

    RS communication

    lockout

    Device off the iComfort bus. Native, expected, first-class on SLP99.

    • i+/i− polarity, one communicating control, indoor and outdoor on the bus. Data, not 24 VAC.
    • Do not convert to 24V. Isolating devices one at a time finds the bad node.
  • E201

    Indoor blower communication

    lockout

    Serial blower dropped off the IFC.

    • Harness, motor power, then motor. This is a communicating VS — same family as EL296V E201, native here.
  • E223 / E225

    Pressure / inducer band

    lockout

    Modulating prove failed at that rate. Stat may say low/high PS even though the hardware is a band, not two EL296 discs.

    • Vent, trap, inducer, hose. 96% PVC physics.
    • Do not treat it as a two-stage W1/W2 swap.
  • E240 / E270

    Flame current / retry lockout

    lockout

    Weak µA or max retries with no flame current.

    • Watch a try. Rod, HSI, gas. Same SureLight ignition as EL296V.
  • E250

    Limit switch circuit open

    warn

    Limit / rollout string. Stat names it in English.

    • Heat CFM follows %. Filter, coil, rise. Rollout is still manual reset.
  • E207 / E290

    HSI / ignitor circuit

    lockout

    Ignitor open or trigger fault.

    • Ohms and 120 VAC during trial. Confirm on the SLP99 door card.

Workflows

SL297NV vs SLP99V

Signature communicating.

  1. SLP99V = modulating percent. SL297NV = two-stage / VS ULN.
  2. iComfort pair first. Then the ULN gas train — not an EL296 orifice.

Test points

i+ / i−
Data, not 24 VAC. One communicating control.
Capacity
Percent on the stat / IFC. Not W1/W2.
Flame
µA per SLP99 card — same F-menu idea if the board exposes it.

Gotchas

  • SL280NV is the 80% Signature ULN cousin — metal vent if the plate says 80%.

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