Lennox Boiler: Overheating
An overheat or high-limit lockout means heat is not leaving the Lennox heat exchanger fast enough — usually a circulation problem (pump, trapped air, closed valve or blockage) or a faulty temperature sensor. Running it repeatedly risks cracking the heat exchanger.
An overheat or high-limit lockout means heat is not leaving the Lennox heat exchanger fast enough — usually a circulation problem (pump, trapped air, closed valve or blockage) or a faulty temperature sensor. Running it repeatedly risks cracking the heat exchanger. On Lennox boilers, this is linked to 2 fault codes (High Limit, Sensor Fault). Below are the likely causes, the safe checks you can make, and exactly what our licensed BC gas technicians do — because boiler repair in British Columbia is licensed gas work, not a DIY job.
Boiler repair is licensed gas work in BC. The checks below are the safe limit of DIY. Do not open the boiler or work on gas, combustion or safety controls — read the fault code, reset at most once, and call a licensed technician if it returns.
What you might notice
- Boiler locks out under load
- Hot or burning smell near the unit
- Heat that starts then cuts out
- Erratic heating or hot-water temperature
- Boiler locks out or refuses to fire
- Wrong temperature shown on the display
Safe checks you can make first
These are the only steps a homeowner should take. If they don’t resolve it, stop — the rest is licensed gas work.
- 1Stop resetting — an overheating boiler can be damaged by repeated firing
- 2Check for obviously closed valves or a silent (failed) pump
- 3Confirm system pressure is normal
- 4Note the fault code and call a technician promptly
Related Lennox fault codes
These Lennox codes are commonly behind “overheating”. Tap any code for its full meaning, causes and fix.
What our licensed technicians do
- Check circulation: pump operation, air-bound zones, closed valves and flow rate
- Inspect the heat exchanger and strainer for blockage or scale
- Test the high-limit and supply/return temperature sensors
- Confirm correct system pressure and bleed trapped air
- Measure sensor resistance against the manufacturer temperature curve
- Inspect wiring, connectors and sensor mounting/contact
Lennox overheating — FAQ
Why is my Lennox boiler overheating or showing a high-temperature fault?
An overheat or high-limit lockout means heat is not leaving the Lennox heat exchanger fast enough — usually a circulation problem (pump, trapped air, closed valve or blockage) or a faulty temperature sensor. Running it repeatedly risks cracking the heat exchanger. The related Lennox fault codes are High Limit, Sensor Fault. A licensed technician confirms the true root cause with the right instruments before any repair.
Is it safe to keep resetting my Lennox boiler when it shows "overheating"?
Reset it at most once. If "overheating" returns, the boiler is telling you there is a real fault that needs diagnosing — continuing to reset it can make things worse. Call GasBoilers.ca at 604-359-1081 and a licensed technician will find the cause.
Can you repair a Lennox boiler with this problem in Greater Vancouver?
Yes. Our Red Seal–certified, TSBC gas-licensed technicians diagnose and repair Lennox GWB8-IH gas-fired hot water boilers across Vancouver, Burnaby, Surrey, Richmond, the Tri-Cities and the rest of Greater Vancouver. Same-day appointments are often available — call 604-359-1081.
“Overheating” on other boiler brands
Lennox boiler overheating? We can help today.
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