Lochinvar Knight XL Outlet ARHL — Outlet Water Temperature Exceeded the Automatic Reset High Limit Setting
Outlet ARHL
Outlet water temperature exceeded the automatic reset high limit setting. The outlet water temperature has exceeded the setting of the automatic reset high limit, so adjust the set point up to a maximum of 200°F, verify the system is full of water and properly purged and piped, check 120 vac to the boiler pump on a call for heat, check the resistance of the water sensors against Table 3-2A, and replace the pump or main control board if necessary.
Applies to
This overheating code is displayed by the Knight XL control (text faults) on Knight XL models (KBX0400 through KBX1000), as documented in Knight XL (KBX) Service Manual, 100383164 Rev C — Table 3-4 fault codes (100383164 Rev C). Codes can differ between controller generations, so always check the manual that matches your unit.
- Lochinvar Knight XL Commercial (KBX)
- Lochinvar Knight XL KBX0400
- Lochinvar Knight XL KBX0500
- Lochinvar Knight XL KBX0650
- Lochinvar Knight XL KBX0800
- Lochinvar Knight XL KBX1000
Controller: Knight XL control (text faults). Source manual: 100383164 Rev C (2025-10).
Why a code is not a diagnosis
An over-temperature code protects the heat exchanger or venting; it does not reveal whether the cause is low water flow, a failed pump, trapped air, fouling or a sensor fault.
Safe things to observe
- Note the code and whether rooms or hot water are still working.
- If you see steam, melted wiring or smell burning, switch the appliance off at its service switch and call a technician.
Do not
- Do not reset the appliance repeatedly while the cause is unknown.
- Do not remove covers or bypass any high-limit device.
How professional service helps
- A technician checks pump operation, flow, system pressure and the cleanliness of the heat exchanger.
- Combustion and safety devices are verified with an analyser and the manufacturer's procedure after any repair.
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Parts and service
Parts commonly involved
These parts appear in the documented text for this alert. A code reports a condition, not a failed part — a technician confirms the cause by testing before anything is replaced.
High-limit switch
A high-limit switch shuts the burner off when boiler water gets hotter than it should, protecting the heat exchanger and the system from overheating.
What a technician checks →Boiler sensors (thermistors)
Boiler sensors are small temperature probes, usually thermistors, that tell the control how hot the water and flue gases are so it can fire safely…
What a technician checks →Control board / PCB
The control board — also called the PCB, or printed circuit board — is the boiler's main computer.
What a technician checks →Circulator pump
The circulator is the pump that moves heated water from a boiler out to the radiators, baseboards or in-floor loops and back again.
What a technician checks →
Service for this alert
- Gas Boiler Repair
Licensed gas technicians from ROMA Heating & Cooling diagnose and repair residential and light-commercial gas boilers across…
Every boiler part explained — what it does, how it fails and what a technician checks.
Documented for Lochinvar Knight XL Commercial (KBX).
Frequently asked questions
Can I clear this code myself?
Clearing a code without fixing its cause usually just brings it back. Note the code, check the safe items on this page, then call a licensed technician. If your appliance manual describes a user reset for this exact code and it stays away, no call may be needed.
Boiler locked out? Call with the alert text ready.
The brand, model and this alert are passed along when you request service online, so the technician arrives prepared.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
- Knight XL (KBX) Service Manual, 100383164 Rev C — Table 3-4 fault codes · 100383164 Rev C · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.