For a Lochinvar KNIGHT boiler, begin with the complete model number and the exact message on its display, then use the service manual for that model and revision. KNIGHT includes multiple boiler families, and their fault labels, diagnostic procedures and compatible parts are not interchangeable. Homeowners can record the fault and note visible symptoms; diagnosis involving gas, electricity, venting, combustion or internal components should be left to a qualified boiler technician.
Start with the model and the exact fault message
Find the full model designation on the boiler nameplate and write down the display message exactly as it appears. If practical, record when the fault occurred and what the boiler was doing, such as attempting to start or running without heating the system. Avoid treating a fault label from another KNIGHT model as a match.
Lochinvar provides documentation by product family and model. For example, its WHB055N page lists Fire Tube documentation, while the KBN106 support page identifies that Water Tube model as discontinued and lists separate family manuals. Use the manual applicable to the boiler’s model and revision:
- Lochinvar WHB055N product and documentation page
- Lochinvar KBN106 support page
The service manuals are technician-facing references. Their diagnostic charts can help explain why a fault needs professional attention, but they are not a safe set of instructions for opening or repairing a boiler.
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What common KNIGHT fault paths point to
A message narrows the area a technician may investigate; it does not by itself prove which component has failed. The examples below come from different Lochinvar manuals and apply only where the message and manual match the boiler.
| Displayed fault or category | Areas the applicable Lochinvar manual identifies | What an operator should do |
|---|---|---|
| “Auto Reset High Limit” (KB-SER-08, models 80–285) | System water and air purging, piping, boiler-pump operation, and relevant sensor or high-limit checks. | Record the message and whether the system is heating. Have a technician assess water circulation and the specified checks. |
| “Delta T High / Delta T Limit” (Fire Tube service manual) | Excessive temperature rise across the heat exchanger; system fill and air purging, hydronic piping, boiler-pump operation, and pump speed or sizing. | Arrange qualified service to investigate flow and temperature conditions; do not open the boiler or adjust pump settings based on a generic guide. |
| “Outlet Temp High / Outlet Temp Limit” (Fire Tube service manual) | System fill and air purging, piping, pump operation, and pump sizing or speed. | Provide the exact fault and model to the service technician. |
| “Fan Low / Fan Speed Low” (KB-SER-08, models 80–285) | Vent or air-intake length or obstruction, wiring, the fan, and control board. The manual defines the fault as actual fan RPM 30% below the requested speed. | Do not dismantle the vent, fan or boiler. Report any visible vent obstruction or damage from a safe location and call a technician. |
| “GV/Relay Fail” (KB-SER-08, models 80–285) | Gas-valve wiring harness, gas valve, and control board. | Do not handle gas-valve wiring or components. Contact a qualified boiler technician. |
These are fault-specific diagnostic leads, not a universal checklist. A similar symptom or differently worded message on another model may have a different meaning.
Rank #2
Safe steps before arranging service
- Record the boiler identity: note the complete model from its nameplate and, if shown, the serial number. Do not remove panels to find it.
- Capture the fault: write down the exact display text and any other visible status information. A photo can help preserve the wording.
- Describe the symptom: note whether heat or hot water is affected, when the message appeared, and whether it returned after a reset. Do not repeatedly reset the unit to keep it running.
- Check only what is safely visible: report obvious external damage or a visibly blocked vent from a safe position. Do not clear, alter or dismantle venting, piping or boiler components.
- Give the information to the service provider: share the model, exact fault, observed symptoms and the manual or documentation page you used. Ask the technician to verify the service manual revision for that unit.
Why internal troubleshooting belongs to a technician
The fault charts can lead into checks of electrical connections, gas valves and relays, venting, combustion-related equipment, pumps, sensors, fuses and control boards. Those procedures may require opening the appliance, electrical measurements or work on gas and combustion systems. Lochinvar’s manuals describe service procedures; they do not make those tasks appropriate for an unqualified operator.
If you smell gas, leave the area and follow your local gas utility’s emergency instructions; do not operate electrical switches in the affected area. For other urgent hazards, follow local emergency guidance rather than attempting boiler diagnosis.
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How to avoid ordering the wrong replacement part
A fault chart mentioning a sensor does not establish a universal KNIGHT sensor part number. Lochinvar’s service documentation directs technicians to compare water-sensor resistance with the applicable manual table and replace a sensor if needed. That diagnosis and any replacement should be matched to the precise model and its parts literature.
Before purchasing any proposed part, have the technician or supplier confirm compatibility against the boiler’s complete model and applicable documentation. A generic search for a “Knight sensor” is not enough to establish fit.
Quick Recap
Rank #4
- 【Compatibility】This ignitor and gasket kit directly replaces PLT3021 and 100165929. It is precision engineered for full compatibility with Lochinvar Knight series boilers, including KB, AW, WB, WH, KBN, SNR, and SNA models. Fits models including KB 80/81 - 500/501, AW 150/151 - 500/501, OK/OA 151 - 801, WB 50/51 - 210/211, WA 125 - 200, SNR126-065, SNR/A150/151-100, SNR200/201-100, SNA285/286-125, SNA400/401-125, SNA500/501-125.
- 【Product Features】The boiler igniter replacement kit Effectively resolves ignition failure, delayed ignition, and boiler no-start issues caused by faulty ignitors, restores your Knight boiler’s normal startup efficiency, avoids frequent shutdowns and service calls, and extends the overall service life of your heating system.
- 【Product Advantages】Built with a high-temperature resistant ceramic insulator and a sturdy metal electrode, this igniter delivers a strong, consistent spark. It effectively resolves common boiler issues, including no ignition, intermittent firing, difficult starting, and spark failure caused by worn electrodes or carbon buildup.
- 【Premium Sealing Gasket】The Ignitor replacement kit comes with a brand-new high-temperature, heat-resistant gasket. The old gasket often deforms, hardens, and leaks after long-term high-temperature operation. Replacing the gasket together prevents flue gas leakage, heat loss, and abnormal combustion, ensuring a fully sealed combustion chamber.
- 【Premium Material】Adopting industrial-grade heatproof ceramic and anti-oxidation metal materials, this boiler part for Lochinvar Knight withstands long-cycle high-temperature boiler operation, resists oxidation, carbon buildup, and thermal aging. It maintains stable ignition performance for long service life even in harsh combustion environments.
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