Worcester Bosch Greenstar CDi Classic Problems — Faults & Fixes
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The Worcester Bosch Greenstar CDi and CDi Classic have earned their reputation as workhorses of the British heating market—millions are installed in homes across the country. However, many of these boilers are now entering their second decade, and age brings predictable wear and tear. Components like ignition electrodes, diverter valves, and pressure vessels don't last forever, and when they start to fail, you'll see fault codes on the display or notice your heating and hot water aren't performing as they should. This guide walks through the most common faults that Gas Safe engineers encounter on ageing CDi boilers, what causes them, and crucially, when a repair makes financial sense and when replacement is the smarter choice. If you spot an error code, smell gas, or your boiler stops firing altogether, contact a Gas Safe registered engineer—DIY fixes beyond basic pressure checks can be dangerous and will invalidate your warranty.
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Most likely cause & what to check
The Worcester Bosch Greenstar CDi and CDi Classic is one of the most widely installed boilers in the UK — millions of homes have one. It has proven to be very reliable, but many installed CDi models are now 10–15 years old and approaching the point where major repairs may not be economical compared to a new boiler. Fault codes and manuals are at worcester-bosch.co.uk/support.
Fault code EA (ignition failure): this is the most common fault on an ageing CDi. First reset once. If EA returns, the ignition electrode is the first thing a Gas Safe engineer will check — on older CDi boilers the electrodes wear and the gap widens, making reliable ignition harder. Electrode replacement is a straightforward and relatively inexpensive repair.
Fault code 227/228 (low pressure): repressurise using the filling loop (two valves underneath or at the side of the boiler). If the CDi was recently serviced and pressure is dropping, look for weeping radiator valves or a failing pressure relief valve — both are common on older systems.
Diverter valve: the CDi combi has a motorised diverter valve that can fail after many years of operation. Symptoms are heating but no hot water (or vice versa), or the boiler firing but not heating either circuit properly. Diverter valve replacement is a common CDi repair — parts are still readily available.
Heat exchanger scale: in hard water areas (the Midlands, South East, South), older CDi boilers accumulate limescale inside the heat exchanger. This causes noisy operation (kettling — a rumbling or banging when firing) and reduced efficiency. A Gas Safe engineer can carry out a power flush or chemical descale, though on very old boilers this may not be worthwhile.
Is repair worth it? If your CDi is over 12 years old and needing significant repair (pump, PCB, heat exchanger), it is often more cost-effective to replace. Modern A-rated boilers are significantly more efficient — a Gas Safe engineer can advise honestly on repair-versus-replace.
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Frequently asked questions
What does fault code EA mean on my Worcester Bosch CDi boiler?
EA indicates an ignition failure—the boiler is struggling to light. On older CDis, the ignition electrodes wear down and the spark gap widens, making reliable ignition harder. A Gas Safe engineer can replace the electrodes, which is usually a straightforward and cost-effective repair.
My CDi boiler keeps showing fault code 227 or 228. What should I do?
These codes mean low system pressure. First, repressurise using the filling loop (the two valves underneath or at the side of the boiler) until the gauge reads 1.0–1.5 bar. If pressure drops again quickly, you likely have a leak—check radiator valve glands and the pressure relief valve, both common culprits on older systems.
I'm getting heating but no hot water—is the boiler broken?
This is often a faulty motorised diverter valve, which is common on CDi combis after years of use. The valve directs water between the heating circuit and domestic hot water, and when it fails, one circuit stops working properly. Fortunately, replacement parts are still readily available and the job is straightforward for a Gas Safe engineer.
My CDi boiler is very noisy and seems less efficient. Is it worth repairing?
In hard water areas, limescale builds up inside the heat exchanger, causing kettling (rumbling or banging) and reduced efficiency. A power flush or chemical descale can help, but on boilers over 12 years old, you may find a new A-rated boiler offers better value—a Gas Safe engineer can advise based on the cost of repair versus replacement.
When should I replace my CDi boiler instead of repairing it?
If your CDi is over 12 years old and needs a major repair (pump, circuit board, heat exchanger, or diverter valve), replacement usually makes better financial sense. Modern boilers are significantly more efficient, reducing your energy bills, and you'll have a warranty—a Gas Safe engineer can give you honest advice on repair versus replace for your specific situation.