The short answer
Worcester Bosch fault codes point to the part of the boiler with a problem. Ignition, flame and overheat codes such as EA, E9 and 224 need a Gas Safe registered engineer. Low pressure codes such as CE 207, 1017 W and H07 can usually be cleared by repressurising. If the pressure keeps dropping afterwards, the system is losing water somewhere.
When a Worcester Bosch boiler runs into trouble, it does not leave you guessing for long. A code appears on the display, the boiler locks out, and the heating goes quiet. Knowing what that code means helps you work out whether you need a Gas Safe registered engineer, a quick top up of system pressure, or someone like us to find out where your water is going.
One thing to be clear about from the start: we are leak detection specialists, not boiler engineers. We do not repair boilers and we never advise anyone to open the boiler casing. We have written this guide because one family of Worcester Bosch codes, the low pressure group, is very often caused by the thing we deal with every week in homes across Devon: a hidden leak on the central heating system.
How Worcester Bosch fault codes work
Worcester Bosch has used a few different display systems over the years. Older Greenstar combi and system boilers (the i, Si and CDi ranges) tend to show short codes such as EA or E9, sometimes paired with a number like 229 or 224. Newer models, including the Greenstar 8000 family, use longer numeric codes such as 1017 W, along with status codes like H07.
The exact list varies between models and production years, so treat any general guide, including this one, as a starting point. Your boiler’s manual has the definitive list for your model, and it is always worth checking the code there before acting on it.
Common Worcester Bosch fault codes at a glance
These are some of the most commonly reported Worcester Bosch codes and their documented meanings. If your code is not listed here, check the manual for your model or ask a Gas Safe registered engineer.
| Code | What it usually means | Who you need |
|---|---|---|
| EA (often shown with 229) | Flame not detected at ignition, or the flame has cut out while the boiler is running | Gas Safe registered engineer |
| E9 (often shown with 224) | Overheat: the boiler’s safety thermostat has tripped | Gas Safe registered engineer |
| A1 | Pump stuck, or running dry with no water passing through it | Gas Safe registered engineer |
| C6 | Fan running at the wrong speed | Gas Safe registered engineer |
| CE 207 | System water pressure too low, often below about 0.7 bar | Repressurise. If it keeps dropping, leak detection |
| 1017 W | Low water pressure, shown on newer Greenstar displays | Repressurise. If it keeps dropping, leak detection |
| H07 | System pressure too low, a warning used on the 8000 series | Repressurise. If it keeps dropping, leak detection |
Meanings vary between models and years, so always confirm a code against your own boiler’s manual.
Ignition and flame codes: EA
EA is the code most Worcester Bosch owners dread, and it sits firmly in Gas Safe territory. It means the boiler tried to light and could not detect a flame, or the flame was lost while the burner was running (this version is often shown as EA 229). Documented causes include an interrupted gas supply, a faulty ignition or flame sensing electrode, and a blocked flue.
In freezing weather there is one cause worth knowing about: a frozen condensate pipe. This is the plastic pipe, usually white and often running down an outside wall, that carries the boiler’s waste water to a drain. If it freezes, the boiler shuts down to protect itself. Gently thawing the pipe with warm water (never boiling) and resetting the boiler once can bring it back. Beyond that, an EA fault is not something to investigate yourself, and we will be honest: it is not a leak detection job either. Book a Gas Safe registered engineer.
Overheat codes: E9 and 224
E9 on older Greenstars, and 224 on newer models, means the boiler’s safety thermostat has tripped because the temperature inside has climbed too high. Documented causes include a failing pump, poor circulation around the system, and a faulty temperature sensor reporting incorrect readings. Because overheating involves the boiler’s core safety systems, the advice is the same as for ignition faults: let everything cool down and call a Gas Safe registered engineer.
We would add one observation from our own work. A system that is repeatedly low on water can struggle to move heat away from the boiler properly. If your overheat fault arrived after weeks of slow pressure loss, mention that history to your engineer, because the two can be connected.
Low pressure codes: CE 207, 1017 W and H07
This is the group you can usually do something about yourself. CE 207 appears on many Greenstar models when the system pressure drops too low, often below about 0.7 bar. On newer displays the same problem shows as 1017 W, and the 8000 series also uses H07 as a low system pressure warning. In each case the boiler is telling you the same thing: there is not enough water in the sealed heating circuit for it to run safely.
Check the pressure gauge first. On most Worcester Bosch boilers it should sit at around 1 to 1.5 bar when the system is cold, though your manual gives the exact figure for your model. If the needle has dropped well below that, repressurising through the filling loop will usually clear the code.
Repressurising a sealed heating system, in general terms:
- Let the system cool fully before you start
- Find the filling loop, usually a braided silver hose or a built-in key or lever beneath the boiler
- Open the valve slowly and watch the gauge climb
- Stop at around 1 to 1.5 bar cold, or whatever your manual specifies
- Close the valve fully, then reset the boiler if the code does not clear itself
- Note the date and the reading, so you can tell how quickly the pressure falls
If the pressure keeps dropping, the water is going somewhere
Here is the part those codes cannot tell you. A sealed central heating system should hold its pressure for months at a time. If you repressurise and the gauge is back down within days or weeks, and CE 207, 1017 W or H07 keeps returning, water is escaping from the system. That is no longer really a boiler question. It is a leak question.
Sometimes the escape route is visible: a weeping radiator valve, a damp joint on visible pipework, or the pressure relief discharge pipe dripping outside. Walk the house and check every radiator and pipe run you can see first. But in many of the homes we visit, nothing shows at all. The leak sits under a floor, inside a screed, behind a wall or along a buried pipe run, quietly letting heating water soak away where you cannot see it.
That is exactly what our central heating leak detection service exists for. We use thermal imaging, acoustic listening equipment, tracer gas and moisture mapping to follow your pipework and pinpoint where the water is getting out, without pulling up floors on a hunch. We cover homes and businesses across Devon, with same-week appointments often available.
What we do, and what a boiler engineer does
The honest division of labour looks like this. Anything involving gas, ignition, the flame, overheating or parts inside the boiler casing belongs to a Gas Safe registered engineer. That covers EA, E9, 224, A1, C6 and any other code that survives a reset. Finding where pressurised water is escaping from the pipework around your home is our job, and it is often the missing piece when a boiler keeps logging low pressure faults that nobody can explain. The two work well together: we pinpoint the leak, the pipe gets repaired, the engineer is happy with the boiler, and the pressure finally holds.
If you are stuck in a loop of topping up and watching the gauge fall, you can read more guides in our articles hub, or get in touch and we will talk it through with you honestly. If we think your problem is one for an engineer instead, we will say so.
Frequently Asked Questions
Boiler Keeps Losing Pressure?
If you keep repressurising your Worcester Bosch and the gauge keeps falling, the leak is there to be found. We trace hidden heating leaks across Devon with minimal disruption, with same-week appointments often available.