Worcester Bosch Fault Codes Explained

Worcester Bosch boilers show a code on the display when they lock out. This page covers the codes we see most often across Hertfordshire and Bedfordshire, using Worcester’s own published wording rather than the definitions that get copied between websites.

Where Worcester publishes something different for different ranges, we say so. Where Worcester does not publish a definition at all, we say that too, instead of inventing one.

EA and 227, flame lockout

The most common Worcester lockout, and the two codes are displayed together on affected appliances. Worcester publishes two different meanings for EA depending on the range: “During operation: flame not detected” in its Engineer’s Service Booklet, and “No gas supply / low gas supply pressure” in the Greenstar i System ErP manual.

Because one of those meanings is a gas supply problem, the first check is free: does your gas hob light?

Full guide to the Worcester EA 227 fault code →

E9, overheat

Worcester’s Engineer’s Service Booklet gives E9 as “Safety temperature circuit has tripped”. The boiler has run hotter than it should and the safety circuit has shut it down.

Check the pressure gauge reads between 1 and 1.5 bar and that your radiators are not all cold at the bottom. A repeat E9 almost always means poor circulation rather than a boiler fault, commonly a failing pump, trapped air, or sludge in the system. Resetting it repeatedly does not address any of those.

C6, fan speed

Worcester’s Engineer’s Service Booklet gives C6 as “Fan speed too low”. The fan is part of the flue safety system, so the boiler will not run without a confirmed fan speed.

There is nothing safe to check yourself on a C6. It is a Gas Safe registered job and it should not be reset around.

If your code is not listed here

Worcester uses different code sets across its ranges, and a code that appears on a Greenstar CDi may not appear in the literature for a Greenstar i or a Highflow. If your display is showing something not covered above:

1. Photograph the display. Note the exact characters and whether anything is flashing.
2. Find your model and serial number, usually on a label behind or beneath the front panel.
3. Do the free checks. Other gas appliances, prepayment meter credit, gas isolation valve, condensate pipe, pressure gauge.
4. Reset two or three times at most, then stop.
5. Have it read against your actual appliance rather than a general list.

We would rather tell you that than publish a definition we cannot stand behind. On a gas appliance a plausible guess is worse than an honest gap, because it sends an engineer looking at the wrong component.

What the free checks are, whatever the code

• Do your other gas appliances work? If the hob will not light, the gas supply is the problem.
• Prepayment meter credit, the most common cause of all and free to rule out.
• Gas isolation valve near the boiler fully open, lever in line with the pipe.
• Condensate pipe not frozen. Thaw with warm, never boiling, water.
• Pressure gauge between 1 and 1.5 bar with the heating off.

Worcester boiler repairs in Hertfordshire and Bedfordshire

Vantage Plumbing & Heating is Gas Safe registered. If your Worcester has locked out and the free checks have not cleared it, we can diagnose the fault against your actual appliance rather than against a list.

Frequently asked questions

What are the most common Worcester Bosch fault codes?

EA and 227 (flame lockout) are the most common by some distance, followed by E9 (safety temperature circuit tripped) and C6 (fan speed too low). Worcester uses different code sets across its ranges, so the code you see depends on your appliance.

What does EA mean on a Worcester boiler?

Worcester publishes two meanings depending on the range: “During operation: flame not detected” in its Engineer’s Service Booklet, and “No gas supply / low gas supply pressure” in the Greenstar i System ErP manual. Check whether your other gas appliances work first.

What does E9 mean on a Worcester boiler?

Worcester gives E9 as “Safety temperature circuit has tripped”. Repeated E9 usually means poor circulation, a failing pump, trapped air or sludge, rather than a fault in the boiler itself.

How many times can I reset a Worcester boiler?

Two or three at most. A boiler that locks out has shut the gas off deliberately, and each reset asks it to send gas to a burner that may not light. If three attempts have not cleared it, further resets will not.

My Worcester is showing a code that is not on this page. What now?

Photograph the display, find your model and serial number, do the free checks, and have the code read against your actual appliance. Worcester code sets vary between ranges and a general list can point you at the wrong component.

When to call an engineer

Still stuck? We repair this fault regularly across Hertfordshire, Bedfordshire and Cambridgeshire. Call 01462 506374 to get an engineer booked, or to talk it through first if you would rather. Genuine 24 hour cover, 365 days a year.

Worcester Bosch fault codes explained in full

We have written up each of these individually, with what the code officially means, what you can safely check yourself and when it needs a Gas Safe engineer.

• Worcester Bosch EA – flame not detected during operation
• Worcester Bosch A1 – pump has run dry
• Worcester Bosch E9 – safety temperature circuit tripped
• Worcester Bosch C6 – fan speed too low
• Worcester Bosch E2 – flow temperature sensor defective
• Worcester Bosch F0 – internal failure
• Worcester Bosch F7 – flame still detected after shutdown
• Worcester Bosch FA – flame detected after the appliance switches off
• Worcester Bosch Fd – reset button pressed inadvertently

Definitions taken from the Worcester Bosch Greenstar CDi Classic engineer’s service booklet. Codes vary between models and generations, so if yours behaves differently, check the manual for your appliance or ring us on 01462 506374.