BoilerFaultCodesWhat the manual says
Manufacturer manualUnderfloorheatingcontactopen
What causes this fault?
This fault occurs when the safety sensor designed to protect your floors detects that the water temperature has become too high. To prevent damage to your flooring, the sensor sends a signal to the boiler to shut down the heating immediately. The most common reasons are a faulty mixing valve, a failed underfloor pump, or a sensor that has become too sensitive over time.
This code is most frequently seen during the first cold snap of autumn when underfloor heating systems are turned on for the first time after being idle all summer.
DIY fix possible
Check if your underfloor heating thermostat is set too high.Ensure the underfloor heating pump is running correctly.Wait for the floor temperature to cool down, as the boiler may restart automatically once the limit thermostat resets.
Avoid the next call-out bill
A cover plan would handle faults like S.39: no call-out fees, no surprise bills.
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