Lennox Boiler: Temperature fluctuating
Heating or hot water that swings hot-then-cold on a Lennox boiler usually means a temperature sensor (NTC / thermistor) is reading incorrectly, or flow through the boiler is unstable. A wrong sensor reading can also mask a real circulation problem.
Heating or hot water that swings hot-then-cold on a Lennox boiler usually means a temperature sensor (NTC / thermistor) is reading incorrectly, or flow through the boiler is unstable. A wrong sensor reading can also mask a real circulation problem. On Lennox boilers, this is linked to 1 fault code (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
- 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.
- 1Note whether it affects heating, hot water, or both
- 2Check system pressure and bleed trapped air from radiators
- 3Look for a sensor or flow fault code
- 4Call us to test the sensors against their temperature curve
Related Lennox fault code
These Lennox codes are commonly behind “temperature fluctuating”. Tap any code for its full meaning, causes and fix.
What our licensed technicians do
- Measure sensor resistance against the manufacturer temperature curve
- Inspect wiring, connectors and sensor mounting/contact
- Confirm actual water temperature with calibrated instruments
- Replace the sensor and verify correct readings across the range
Lennox temperature fluctuating — FAQ
Why does my Lennox boiler's temperature keep fluctuating?
Heating or hot water that swings hot-then-cold on a Lennox boiler usually means a temperature sensor (NTC / thermistor) is reading incorrectly, or flow through the boiler is unstable. A wrong sensor reading can also mask a real circulation problem. The related Lennox fault code is 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 "temperature fluctuating"?
Reset it at most once. If "temperature fluctuating" 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.
“Temperature fluctuating” on other boiler brands
Lennox boiler temperature fluctuating? We can help today.
Licensed, Red Seal–certified gas technicians across Greater Vancouver. Upfront pricing, same-day service available.