Boiler Overheating
A boiler that overheats will typically shut itself down as a safety measure — the overheat thermostat trips and the boiler locks out until it cools enough to reset. While this safety mechanism protects your boiler from damage, repeated overheating indicates a real fault that needs professional diagnosis.
Common causes of overheating include a failing circulation pump, blocked plate heat exchanger, faulty thermistor sending wrong temperature readings, or a stuck motorized valve restricting flow. Our gas-certified technicians diagnose the exact cause and fix it fast — often the same day.
What Causes Boiler Overheating
Overheating occurs when heat isn't being carried away fast enough by the circulating water. This happens when flow is restricted (blocked heat exchanger, failing pump, closed valve) or when the boiler's temperature sensors or controls malfunction (faulty thermistor, stuck gas valve, PCB fault). The boiler's overheat thermostat is the last line of defense — it trips to prevent damage.
Our Overheating Diagnostic Process
We measure flow and return temperatures to quantify the temperature differential, check pump performance, inspect the heat exchanger for blockage, and test thermistors for correct resistance values. We also check that all isolation valves are fully open and that the system pressure is within range. A fixed written quote is provided before any repair work.
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.
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