Lochinvar Stack High Limit: Stack (Flue) High Limit
What the Lochinvar Stack High Limit fault means, what causes it, and why it's a job for a licensed BC gas technician — not a DIY reset.
Severity
High — needs prompt professional attention
Gas safety first
This fault involves gas, combustion or venting. If you smell gas (rotten-egg odour), hear hissing, or feel unwell, leave the building immediately and call 911 or FortisBC at 1-800-663-9911 from outside. Do not flip switches or relight anything. For all other cases, switch the boiler off and call a licensed gas technician.
What the Lochinvar Stack High Limit fault means
The flue/stack temperature exceeded its limit, pointing to a combustion or heat-exchanger problem.
On Lochinvar Knight, WHN and SMART System series, Stack High Limit is a air-pressure / venting fault. It is a protective response — the boiler is telling you something needs attention, and the safe, lasting fix is a proper diagnosis rather than repeated resets.
Symptoms you may notice
- Lockout, often worse in wind, rain or cold snaps
- No heat or hot water
- Boiler tries to start, then faults during purge
Common causes of Lochinvar Stack High Limit
Why this is not a DIY fix
Air-pressure-switch and flue faults are a combustion-safety issue: a blocked, disconnected or leaking vent can spill flue gases — including carbon monoxide — into your home. This must be inspected and corrected by a licensed gas technician, never patched or bypassed.
In British Columbia, gas work must be performed by a TSBC-licensed gas fitter. GasBoilers.ca — a CanroHeat division — sends Red Seal–certified, gas-licensed technicians who diagnose the true cause, repair it correctly, and verify safe operation before they leave.
How our technicians diagnose & repair it
- 1Inspect intake and exhaust venting for blockage, sagging or disconnection
- 2Test the air-pressure switch and its sensing tubes for blockage or condensate
- 3Check the condensate trap and flue for water back-up
- 4Verify safe combustion and draft with analysis before return to service
Related Lochinvar codes
Lochinvar Stack High Limit — FAQ
What does the Lochinvar Stack High Limit fault mean?
The flue/stack temperature exceeded its limit, pointing to a combustion or heat-exchanger problem. On Lochinvar Knight, WHN and SMART System series, this is categorised as a air-pressure / venting fault.
What causes Lochinvar Stack High Limit?
The most common causes are: Scaled/fouled heat exchanger; Combustion out of spec; Flue restriction. A licensed technician confirms which one applies before any part is replaced.
Can I fix Lochinvar Stack High Limit myself?
No. Air-pressure-switch and flue faults are a combustion-safety issue: a blocked, disconnected or leaking vent can spill flue gases — including carbon monoxide — into your home. This must be inspected and corrected by a licensed gas technician, never patched or bypassed. Repeatedly resetting the boiler without fixing the root cause can be unsafe and can cause further damage. Call GasBoilers.ca at 604-359-1081 for a licensed diagnosis.
Is the Lochinvar Stack High Limit fault dangerous?
It can be. This fault involves combustion, gas or venting. If you ever smell gas, leave the building immediately and call 911 or FortisBC at 1-800-663-9911 from outside. Otherwise, switch the boiler off and book a licensed technician.
How much does it cost to fix Lochinvar Stack High Limit in Greater Vancouver?
Cost depends on the root cause and any parts needed. We start with a flat-rate diagnostic, then quote the repair before any work begins — no surprises. Call 604-359-1081 for current pricing and same-day availability.
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