Lennox Furnace: Poor ignition or loud combustion resonance – Lennox SL280UHNV

Poor ignition or loud combustion resonance - Lennox SL280UHNV on a Lennox furnace: SL280UHNV (ultra-low NOx air/gas burner) has trouble lighting or lights with a loud resonance. Hard ignition means too much combustion air (air orifice too large); resonance means too little air.

Homeowner with a furnace problem? Call (647) 657-2977 or book a service call — licensed technicians across Vaughan and the GTA.

Applies to: Lennox SL280UHNV 80% communicating furnaces: SL280UH060NV36A, SL280UH080NV48B, SL280UH080NV60C, SL280UH100NV60C

Common causes of poor ignition or loud combustion resonance - lennox sl280uhnv

• Wrong or loose air orifice
• Plugged air inlet screen
• Vent/air intake restriction
• Kinked, loose or plugged signal hoses to gas valve
• Gas valve out of range
• Low supply voltage or gas pressure (-05 models)

How to fix poor ignition or loud combustion resonance - lennox sl280uhnv: step by step

1. 05 and later: confirm incoming voltage is 108-132 V and gas supply pressure is 5-14 in. w.c.; fix power or gas supply first.
2. On -01 to -04 (not -040), make sure the inducer was slowed to 4300 RPM. If it wasn't, call your Lennox service rep.
3. Check the air orifice (inside the gray coupling between the clamps): correct size per the orifice table, fully seated against the elbow, and air inlet screen clear.
4. Check manifold pressure (-01 to -04 Table 18/19; -05 Table 23 0.0-0.10 in. w.c.). The gas valve is not adjustable - if manifold is out of range, replace the gas valve.
5. If manifold is OK, check signal / system operating pressure (-05 Table 24). In range and still a problem: replace the air orifice; out of range: check vent/intake restriction, inlet screen and signal hoses.
6. If pressure still wrong after fixing restrictions, replace the gas valve.
7. Ignition problem after all checks: fit the 'difficulty igniting' (smaller) air orifice. -05 resonance: install Low Profile Combustion Air Intake Kit 25B23 (-01 to -04: fit the 'resonance' larger orifice).

If the unit shows an error code, look it up: Lennox Furnace codes

Models

Lennox EL195UHNE

EL195UH040NE36BEL195UH060NE36BEL195UH080NE48CEL195UH100NE60C

EL296UHV

EL296UH045XV36BEL296UH070XV36BEL296UH090XV36CEL296UH090XV48CEL296UH090XV60CEL296UH110XV48CEL296UH110XV60CEL296UH135XV60D

Lennox ML180UHE

ML180UH045E36AKML180UH045XE36AKML180UH070E36AKML180UH070E36BKML180UH070XE36AKML180UH070XE36BKML180UH090E48BKML180UH090E60CKML180UH090XE48BKML180UH110E60CKML180UH110XE60CKML180UH135E60DK

Lennox SL280UHV

SL280UH060NV36ASL280UH070V36ASL280UH080NV48BSL280UH080NV60CSL280UH090V36BSL280UH090V48BSL280UH090V60CSL280UH100NV60CSL280UH110V60CSL280UH135V60D

Lennox SL297NV

SL297UH040NV36BSL297UH060NV36BSL297UH080NV48CSL297UH080NV60C