Quick Answer
A Worcester Bosch fault code is the boiler telling you what it has detected. Most Greenstar models show a fault code plus a cause code, such as EA 229, and the pair identifies the problem. Every meaning on this page comes from the official Worcester Bosch manuals.
EA 227 means no flame signal after ignition. EA 229 means the flame was lost while running. E9 224 means the flue or high limit thermostat has activated. A1 281 means the pump is stuck or running dry. Low pressure shows as 1017 on the Greenstar 4000 and 2971 on the 8000 Life.
You can safely read the code, check the pressure gauge, thaw an accessible condensate pipe with warm water and press reset once. Anything involving gas or the sealed casing is Gas Safe work. A weekday daytime diagnostic visit with us costs £120.
Codes differ between Worcester Bosch generations, so your own manual has the final word. This guide says which model each code comes from.
Key Takeaways
- Read both parts: The Greenstar i ErP shows a fault code and a three-digit cause code together. Write both down before you search or ring anyone.
- Flame codes come first: EA 227 and EA 229 cover failed ignition and lost flame. The official checks include gas pressure, the flue, the flame probe and blocked condensate pipes.
- Safe homeowner actions: Read the code, check the gauge, top up to 1 to 1.5 bar, thaw an accessible condensate pipe with warm water, and press reset once.
- The Gas Safe boundary: Opening the sealed casing, adjusting a gas valve or testing the circuit board is Gas Safe work, whatever the code says.
- Fixed diagnostic prices: £120 weekday daytime, £160 Saturday, £180 evening and £220 for emergency or out of hours. We quote every repair before starting.
How to read a Worcester Bosch fault code
A Greenstar i ErP display has two parts. First comes a letter code such as EA or E9. Next is a three-digit cause code such as 227 or 224. Together they identify the fault. Write down both.
The Greenstar i ErP manual splits faults into two kinds. A blocking error stops the boiler temporarily and clears by itself once the condition resolves. A locking error shuts the boiler down until it is reset. The boiler also keeps a history of recent faults, which an engineer can read.
Codes that begin with H are maintenance messages, not breakdowns. H03 means the operating hours set for the service interval have run out. It works like a service light in a car. A boiler service and a reset of the reminder clears it.
Codes change between generations. Identical letters can carry different cause codes on different models. Newer boilers label them differently too. The Greenstar 8000 Life manual tags each cause code with B for blocking or V for locking. Not sure which manual is yours? Start with the Worcester Bosch troubleshooting tool.
EA 227 and EA 229: the boiler will not light or loses its flame
EA 227 is “no ionisation detected after ignition”. The boiler tried to light and no flame signal followed. EA 229 is “loss of ionisation signal during operation”. The flame lit and then went out.
The Greenstar i ErP manual tells the engineer to check the dynamic gas pressure, the flue for restrictions, the gas-air ratio, the ignition unit, the gas valve, contamination in the appliance and blocked condensate pipes. The Greenstar 8000 Life manual adds the ceramic insulator on the spark electrode, the flame sense probe and its lead. It also lists a frozen condensate pipe.
Most of that list is gas and combustion work. Two items are yours. Check that other gas appliances work, such as the hob, and that a prepayment meter has credit. Then check whether an external condensate pipe has frozen in cold weather. The thawing steps are in the DIY section below.
Reset once if the manual allows it. If EA 227 or EA 229 comes straight back, stop. A repeated lockout is the boiler protecting you, and pressing the button again does not fix the cause. Leave it off.
E9 224 and E9 276: the safety thermostat has tripped
E9 224 means the flue or high limit thermostat has activated. E9 276 means the primary flow temperature went above 95 degrees Celsius. Both are protective shutdowns. Do not keep resetting them. The boiler got too hot, or heat could not leave the heat exchanger fast enough.
The manual checks are about water, not gas. They cover system water pressure, air in the system, circulation and the pump. The 8000 Life manual also asks for the lead on the safety temperature limiter and any blockage that restricts flow.
Look at the pressure gauge first. The manual lists system water pressure as its first check. If the gauge is low, repressurise as described below and reset once. If the gauge is normal, call us. A tripped limiter on a boiler with normal pressure points to a pump, flow or sensor fault that needs testing with the right equipment.
A1 281: the pump is stuck or running dry
Worcester Bosch describes A1 281 as “pump stuck or running dry”. The boiler is asking for water to circulate and the pump is not moving it. Its checks are flow pressure in the system, air in the system and the pump itself. On the Greenstar CDi Classic, the first check for A1 is whether system pressure has fallen below 1.2 bar.
Check the gauge. If pressure is low, topping up can clear it. If pressure is fine and the code stays, the pump rotor may be seized or the pump may have failed. That is an engineer repair. A pump left to run dry damages itself and the heat exchanger.
Low pressure codes: 1017, 2970 B and 2971 B
Low pressure is the one fault you can often fix at home. The code depends on the model.
The Greenstar 4000 user instructions show “Fault 1017: System pressure too low” when the gauge reads below 0.8 bar. On the Greenstar 8000 Life, 2971 B is “system pressure too low” and 2970 B is “pressure drop in heating system too rapid”. Older boilers have no dedicated low pressure code. The Greenstar i ErP fault table has none. The Greenstar CDi Classic service booklet has none either, and the Greenstar 24i and 28i Junior user guide shows faults only as flashing lights, with no display code at all. On those models the gauge is your only warning.
Most boilers want 1 to 1.5 bar cold. The Greenstar 4000 manual shows a green zone of 0.8 to 1.7 bar. Check your own manual for the target. It varies.
Topping up once or twice a year is normal. More often is not. If you top up and the code returns within days, water is escaping somewhere. Our boiler losing pressure guide covers the causes. A pressure that jumps when the heating runs and then falls to zero when it cools often means a flat expansion vessel.
The other codes you might see
These codes are diagnostic. They tell the engineer which component to test. Each card shows what the official manual says and what is safe for you to do.
Flame sensing codes: F7 228 and FA 306
Gas Safe OnlyF7 228 means ionisation current was detected before the burner started. FA 306 means ionisation was detected after the gas valve closed.
Nothing at the boiler. Do not keep resetting FA 306.
As soon as either code appears and stays.
Inspect and replace the ionisation probe, check the condensate is discharging, then test the gas valve coils.
Fan codes: C6 215, C6 216, C7 214 and C7 217
Fan FaultC6 means fan speed too high (215) or too low (216). C7 means the fan did not run at start up (214) or stopped during operation (217).
Reset once. Nothing else is safe to touch.
If the code returns. The boiler cannot burn gas safely without its fan.
Check the fan wiring and connector, test for 230 volts at the fan, then replace the fan or control box if needed.
Sensor and temperature codes: E2 222, E2 223, A7 808 and D4 341
Sensor FaultE2 means the flow temperature sensor is shorted (222) or disconnected (223). A7 808 is a domestic hot water sensor defect. D4 341 means flow temperature is rising too fast.
For D4 341, check every radiator valve is open and the pressure gauge reads normally.
For E2 and A7, straight away. For D4, if open valves and normal pressure do not clear it.
Test the sensor harness and the sensor itself, then check circulation, air in the system and the pump.
Control box codes: F0 238, EA 261 and Fd 231
Control FaultF0 238 is a gas valve or control box error. EA 261 means the heat cell module is potentially defective. Fd 231 means power was interrupted during a lockout.
Reset once as your manual describes. For Fd 231, note which lockout code came before it.
If F0 238 or EA 261 returns after a reset.
Test the gas valve coils for 230 volts, check the module is seated properly, and replace the control box if the voltage is present.
Worcester Bosch Fault Code in West London?
Our Gas Safe registered engineers (657972) diagnose flame, pressure, fan and overheat lockouts. Tell us the code and your model, and we arrive knowing where to start.
What a fault code diagnosis costs
Our diagnostic rates are fixed and published. The rate depends on when we attend, not on which code is showing.
The £120 rate covers weekday daytime visits only. It does not cover weekends, evenings or emergencies, which use the rates above.
Our phone line is answered 24/7 by an AI receptionist who takes your details at any hour. Routine visits run in two arrival windows, 08:00 to 12:00 and 12:00 to 18:00 across Ealing, Acton, and surrounding neighbourhoods. We dispatch genuine emergencies at any time at the £220 rate, but routine faults wait for a scheduled window.
If the same code keeps returning, the Homeowner Plan at £9.99 a month adds the standard annual service, priority booking and 10% off labour.
What you can safely do yourself
Your manual decides what is safe for your model. These actions are the ones the manuals themselves allow.
Read and record the code. Note the letter code and the cause code. A photo of the display helps us.
Check the power and the controls. Make sure the fused spur next to the boiler is switched on. If your room thermostat is wireless, replace its batteries.
Check the pressure and top it up. Look at the gauge with the boiler cold. If it is low, use the filling loop until it reads 1 to 1.5 bar, then close the valve fully. Look at your boiler to see which filling control you have. Some have a blue keyless lever on the boiler itself. Others use a filling loop with a key. Follow your manual for the open and close steps. Leaving the filling control open pushes pressure towards 3 bar and forces the pressure relief valve to discharge.
Thaw an accessible frozen condensate pipe. The condensate pipe carries acidic water from the boiler to a drain. In a hard frost an external section can freeze and shut the boiler down. The Greenstar 4000 manual allows you to thaw it only if it is at ground level and easy to reach. Hold a hot water bottle or a cloth soaked in hot water against the pipe near the blockage. You can pour hot water from a watering can. Never use boiling water, because it can crack the plastic. Mind the slip hazard where the water freezes on the ground. Then reset the boiler and wait two or three minutes.
Press reset once. Do this after you have dealt with a clear cause. Same code again? Stop.
When to stop and call a Gas Safe engineer
If you smell gas or suspect carbon monoxide, call the National Gas Emergency Service on 0800 111 999 first. Leave the property, open doors and windows on the way out, and do not touch any electrical switches. Do not use a naked flame. Do not turn the gas back on until an engineer has checked it. The Gas Safe Register emergency guidance sets out the steps.
For every other fault, the line is the sealed casing. Under the Gas Safety (Installation and Use) Regulations 1998, gas work must be done by a Gas Safe registered engineer. That covers opening the room-sealed casing, adjusting a gas valve, testing the circuit board wiring and cleaning the burner. A boiler that locks out is protecting itself. Bypassing that protection is unsafe.
Call us if the same code returns after one reset. Call us for any E9 that returns with normal pressure, any C6 or C7 fan code, and any FA, F7 or F0 code. You can check any engineer’s registration at the Gas Safe Register before you let them in. Ours is 657972.
What our engineer does on the visit
The order matters. It saves time and money.
- Read the display and the fault history. The code tells us where to start. The history shows whether it is a one-off or a pattern.
- Check power first if the display is dead. We put a non-contact voltage tester on the incoming supply cable. That separates a supply fault from a blown fuse or failed board inside the boiler.
- Check pressure and look for water. On Worcester Bosch boilers we look at the pressure relief valve and the expansion vessel. A flat vessel makes pressure surge and pushes the relief valve open. Debris can then stop the valve seating again, which is more likely on a boiler that has missed its annual service. We also inspect the plastic hydraulic manifolds. Thermal cycling and water hammer can cause pinhole leaks, particularly where no shock arrestor is fitted on the cold mains.
- Run the tests the manual lists for your code. For EA codes that means gas working pressure, the ignition and flame probe, the condensate route and the gas-air ratio where required.
- Quote before we repair. You get a fixed written price for parts and labour before any work starts. If the boiler is old and has needed several major repairs in two years, we will tell you honestly when a new boiler installation makes more sense.
Problems that look like a fault code
A blank display is not a fault code. It usually means no power. Our no heating or hot water guide covers that sequence.
Radiators that stay cold with a normal display and no code point to controls or circulation, not gas. Hot water with no heating, or the reverse, usually means a valve or control fault rather than the burner. If the boiler fires for one demand, the burner, fan and gas valve are working.
Some older boilers have no low pressure sensor. They keep running with almost no water, and the damage shows up later. Check your gauge every month, code or no code. It takes seconds.
Frequently asked questions
What does EA 229 mean on my Worcester Bosch boiler?
EA 229 means the boiler lost its flame signal while running. The flame lit and then went out, so the boiler locked out for safety. The manual lists gas pressure, the gas-air ratio, the flame probe and wiring, and blocked condensate pipes as checks. Check for a frozen condensate pipe, reset once, and call a Gas Safe engineer if it returns.
Can I fix a Worcester Bosch fault code myself?
Only the simple ones. You can repressurise a low system, thaw an accessible frozen condensate pipe with warm water, replace thermostat batteries and press reset once. Anything involving gas, combustion, the fan, the gas valve or the sealed casing must be done by a Gas Safe registered engineer. If the code keeps returning after one reset, stop and book a diagnostic visit.
Is it safe to keep using my boiler if it shows a fault code?
It depends on the code. A locked-out boiler has shut itself down for safety, so do not bypass it. If you smell gas or suspect carbon monoxide, call 0800 111 999 straight away and leave the property. For a pressure code you can top up and carry on. For flame, fan or overheat codes that keep returning, leave the boiler off until it is checked.
How much does it cost to have a Worcester Bosch fault code diagnosed?
A weekday daytime diagnostic visit costs £120. Saturday daytime is £160, evenings from 18:00 to 21:00 are £180, and emergency or out of hours dispatch is £220. Any repair is quoted as a fixed price before work starts, so you know the full cost before agreeing. The code you are seeing does not change the diagnostic rate.
Why does my Worcester Bosch keep showing a low pressure code?
Topping up once or twice a year is normal. If the code returns within days, water is escaping or the expansion vessel has lost its charge. The code is 1017 on the Greenstar 4000 and 2971 B on the 8000 Life. Top up to 1 to 1.5 bar, close the loop fully, and have the cause traced if pressure keeps falling.
How many times can I press reset on a Worcester Bosch?
Once. Press reset after dealing with a clear cause such as low pressure or a frozen condensate pipe. If the same code comes straight back, stop pressing it. Repeated resets do not fix the fault, and they hide the pattern an engineer needs to see. Write down the code and cause code and book a diagnostic visit instead.
What does E9 mean and why does it keep coming back?
E9 224 means the flue or high limit thermostat activated, and E9 276 means the primary flow temperature went above 95 degrees Celsius. Both are overheat shutdowns. Common causes in the manual are low pressure, trapped air, a failing pump and restricted flow. Check the gauge once. If pressure is normal and E9 returns, call an engineer.
Are Worcester Bosch fault codes the same on every model?
No. Codes and cause codes differ between generations. A Greenstar i ErP uses a letter code plus a three-digit cause code. A Greenstar 4000 shows a four-digit code such as 1017 with a text message. On the 8000 Life, cause codes carry a B or V. Use your own boiler manual, or tell us your model and we will check it.
Code meanings are taken from the Worcester Bosch Greenstar i ErP installation and servicing instructions (6 720 806 944), the Greenstar 8000 Life installation and maintenance instructions (6720883865) and the Greenstar 4000 user instructions (6 720 891 170), checked October 2026. Codes vary by model family. Gas emergencies: National Gas Emergency Service 0800 111 999.
