BoilerFaultCodes.com

Worcester Bosch 25si and 28si Fault Codes

Combi Natural GasLPG 25-28 kW 2001-2005 Discontinued
GC Numbers: 47-108-0947-108-10

Replaced by: Greenstar 25Si and 30Si

This boiler uses indicator light combinations

Note which lights are on, off, or flashing and at what speed. Match the combination to the table below. Do not reset until you have noted the pattern. How to read fault codes →

Most common fault codes

2 lights flashing fast
Your boiler has failed to ignite properly, meaning it cannot create the flame needed to heat your home or water.
Gas Safe engineer required · £120-350
Central heating and hot water demand indicators flash together
Your boiler has switched itself off for safety because the internal water temperature has become too hot.
May be DIY safe · £100-280
Central heating demand indicator flashes slowly (approximately once per second)
Your boiler has tried to light itself five times and failed, so it has shut down for safety purposes.
May be DIY safe · £100-£350

All 18 fault codes

Code Severity Plain English
2 lights flashing fast High Your boiler has failed to ignite properly, meaning it cannot create the flame needed to heat your home or water.
Central heating and hot water demand indicators flash together High Your boiler has switched itself off for safety because the internal water temperature has become too hot.
Central heating demand indicator flashes slowly (approximately once per second) High Your boiler has tried to light itself five times and failed, so it has shut down for safety purposes.
Domestic water demand indicator flashes (approximately five times per second) High Your boiler has detected an issue with how it extracts exhaust fumes, and it has shut down for safety purposes.
FAIL POINT A High Your boiler has lost power because it is switched off at the front, there is no electricity reaching the unit, or an internal fuse has blown.
FAIL POINT B High Your boiler has suffered an electrical failure that has caused it to lose power and stop providing heating and hot water.
FAIL POINT C High Your boiler’s internal control system has suffered an electrical component failure and can no longer manage the heating process.
FAIL POINT D High Your boiler is not receiving a signal from your thermostat or internal timer telling it to turn on.
FAIL POINT E High Your boiler has detected a problem with the internal sensor that tells it when to provide hot water, meaning you currently have no hot water when you turn your taps on.
FAIL POINT F High Your boiler has likely detected that it is too cold to operate safely or that moisture has affected its internal electronics.
FAIL POINT G High Your boiler has shut down because it has reached a temperature that is too high, often due to a lack of water or a circulation issue.
FAIL POINT H High Your boiler has stopped working because it cannot light the flame, which means you currently have no heating or hot water.
FAIL POINT I High Your boiler has detected an electrical issue with one of its internal sensors or the gas valve, causing the system to shut down for safety.
FAIL POINT J High Your boiler has detected a problem with how air and waste gases are moving through the system, causing it to shut down for safety.
FAIL POINT K High Your boiler's main internal computer has developed a serious communication error and cannot operate, often because it has been exposed to water or has suffered an electrical failure.
FAIL POINT L High Your boiler has likely been left in a testing mode during a service, or it is struggling to control the temperature of your hot water properly.
Fast flash High Your boiler has detected a general internal fault that requires a system reset or power cycle to clear.
Slow flash High Your boiler has detected a safety-related issue and has locked itself out to prevent further damage, requiring a manual reset to restart.

Worcester Bosch 25si and 28si is discontinued — time for a new one?

Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.

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