Troubleshooting
Combi Boiler Short-Cycling (Firing On and Off)
Rapid on-off cycling wastes fuel and wears components.
Short-cycling is when a boiler fires up, runs briefly, shuts off, and quickly repeats. It's often caused by an oversized boiler, poor circulation, a faulty sensor, or system sludge — and it increases wear and fuel use over time.
A technician can identify whether it's a sizing, circulation or control issue.
Common causes
- Boiler oversized for the heat demand
- Poor circulation or partial blockage
- Faulty thermostat or sensor
- System sludge restricting flow
- Incorrect control settings
This is not a DIY repair
Combi boilers are gas-fired appliances regulated under the BC Safety Standards Act. Opening the unit, touching the gas valve, or working on the flue without a valid BC gas-fitter licence is both unsafe and illegal. Diagnosing the fault is helpful — fixing it should always be left to a certified technician.
Call 778-909-5731Related symptoms & help
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