Combi Boiler Overheating

Overheat lockouts protect the heat exchanger — but the cause must be fixed.

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Licensed & Insured Gas-Certified Technicians Serving Vancouver Since 1999

An overheating combi boiler will trip its high-limit safety and lock out. The most common causes are poor water circulation (a failing pump or airlock) and limescale or sludge insulating the heat exchanger so heat can't transfer away.

Repeated overheating damages the heat exchanger — one of the most expensive parts — so prompt diagnosis is worthwhile.

Common causes

Failing circulation pump
Airlock or closed isolation valve
Limescale on the heat exchanger
Sludge restricting flow
Faulty temperature sensor

Smell gas or suspect carbon monoxide? Leave now.

If you smell gas, hear hissing, or your CO alarm sounds, leave the building immediately and call your gas utility's emergency line from outside. Do not operate switches or relight the appliance. Once you are safe, call us for a licensed repair.

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