BoilerFaultCodesWhat the manual says
Manufacturer manualSafety Thermostat Operated / overheat of the primary water
What causes this fault?
This fault occurs when the internal safety sensors detect that the water inside the boiler has reached a dangerously high temperature. It is usually caused by a failure in the pump preventing water from moving through the system or a blockage that is trapping heat within the heat exchanger.
This issue often surfaces during the first cold spell of autumn when the heating is turned back on after sitting idle all summer, which can cause the internal pump to seize.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like E110: no call-out fees, no surprise bills.
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Related fault codes
All 21 fault codes on the Promax HE Store
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