Low Information
P4 on Worcester Bosch Greenstar 25HE

Your boiler is currently running its own internal health check as it starts up and may just need a moment to finish.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description

Part of the self-test sequence sequence when the appliance is switched on.

What causes this fault?

This occurs when the boiler is performing a routine electronic check of its internal components immediately after being powered on. It is a programmed safety sequence designed to ensure all sensors and controls are responding correctly before the burner ignites. Most often, the code will clear itself within seconds once the software confirms the system is safe to operate.

This code may be seen more frequently following a power cut, which are more common during stormy winter weather.

DIY fix possible

Wait up to 10 minutes for the self-test to completeEnsure the power cycles correctly if you have recently turned the boiler off and onMonitor the display to see if it transitions to a normal temperature reading

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