BoilerFaultCodesWorcester Bosch No DHW function (CH OK) Fault Code
Also written as NODHWFUNCTIONCHOK — same fault.
The Worcester Bosch No DHW function (CH OK) fault code means: your boiler is providing central heating but is failing to detect when you turn on a hot tap, meaning you have no hot water.. It appears on 1 Worcester Bosch model in our database.
Technical description: Flow sensor failure. DHW sensor (LED 4 flash/second). Board fault.
What causes the Worcester Bosch No DHW function (CH OK) fault?
This fault occurs when the boiler's internal sensors fail to detect water moving through the system when you open a tap. The most common reason is that the plastic turbine inside the flow sensor has become stuck with limescale or debris, preventing it from sending a signal to the boiler to fire up for hot water. In some cases, the temperature sensor has simply worn out and is providing an incorrect reading that tricks the system into staying off.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the No DHW function (CH OK) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch No DHW function (CH OK) fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026