BoilerFaultCodesWhat the manual says
Manufacturer manualDHW demand. The domestic hot water demand is activated.
What causes this fault?
This code is triggered when your boiler detects water flowing through your hot water pipes. It is a signal that the internal flow sensor has spotted a demand for hot water, prompted by someone opening a tap or starting a shower. The boiler is not broken; it is simply communicating that it is busy heating your water.
This status is slightly more common in winter when incoming mains water is much colder, meaning the boiler has to work at full power for longer to reach your desired temperature.
DIY fix possible
Turn off all hot water tapsCheck that the code changes to a different status (like S.0 or S.4)If the code stays on despite all taps being closed, check for a dripping tap or a leaking pipe
Avoid the next call-out bill
A cover plan would handle faults like S.20: no call-out fees, no surprise bills.
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Related fault codes
All 148 fault codes on the ecoTEC Pro 28
Seeing a different code? Every code this model can display, in one place.