Worcester Bosch EA 234 fault codewhat it means and how to fix it
The control board cannot see the gas valve coil, so it will not attempt to light. Worcester call it a gas valve error, coil disconnected. No gas is released, but it is a gas job.
Take care
Get a Gas Safe registered engineer to look at your Worcester Bosch EA 234
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What EA 234 means
The Compact family manuals list EA 234 as "gas valve error — gas valve coil disconnected", and it is one of the few codes in the ignition group where the boiler has not tried to light at all. Before the sequence starts, the board checks that the gas valve's solenoid coils are electrically present.
If the circuit to a coil is open — a connector off the valve, a broken wire in the harness, or a coil that has failed — the check fails and the boiler stops with 234 rather than sparking into a valve it cannot operate. That makes it a safer failure than the other EA codes, which is why it is rated caution rather than danger, but it is not a fault you can reach: the gas valve sits behind the case on the gas side of the appliance, and disturbing its wiring or connectors is work for a Gas Safe registered engineer who will leak-test afterwards. The parallel entries in Worcester's tables are worth knowing about.
F0 238, on the Greenstar i, is "gas valve or control box error", with the engineer checking for 230 V across the blue and orange wires to the coils, and FA 306 is a flame detected after the valve has closed, which is the opposite problem — a valve that will not shut. A boiler showing 234 has typically either just had work done that disturbed the valve connector, or has a valve at the end of its life.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Gas valve connector off or loose | The plug onto the valve can be knocked during a service or a pump change and sit half-home, which reads as an open coil. | Common |
| Failed solenoid coil | Worcester's CDi Classic service booklet gives coil resistances to be measured; a coil reading open circuit has failed and the valve is replaced as a unit. | Common |
| Harness damage | A wire chafed against the case or a corroded terminal in the harness between board and valve breaks the circuit intermittently. | Occasional |
| Control board output fault | If the coils and wiring test correctly, the board's gas valve drive is at fault and the board is replaced. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£90–£480
Time on site
1 hour
Reconnecting or repairing the coil wiring £90–£160. Gas valve replacement £300–£480 fitted including the leak test.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Worcester Bosch Greenstar gas valve
£180–£320Authorised Worcester parts distributor
Price checked 28 September 2026
Worcester Bosch Greenstar control board (PCB)
£250–£450Authorised Worcester parts distributor
Price checked 28 September 2026
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Related Worcester Bosch fault codes
- EA 227Stop — call an engineerThe boiler tried to light and never detected a flame, so it has shut the gas off and locked out. This is the most common Worcester fault code.Related: ignition and gas supply
- EA 229Get it checkedThe burner lit and then the flame was lost during operation. That is a different fault from failing to light in the first place.Related: ignition and gas supply
- F7 228Stop — call an engineerA flame is being detected before the burner has started. Switch the appliance off and get a Gas Safe engineer rather than resetting.Related: ignition and gas supply
- FA 306Stop — call an engineerThe boiler detected a flame after it had closed the gas valve. That points to a valve letting gas past when it should be shut, and it must not be reset.Related: ignition and gas supply
- 2951Stop — call an engineerThe flame has been lost too many times in a row and the boiler has locked out. Each loss was a 229; Worcester's instruction is to read the history and find what put it out.Related: ignition and gas supply
- EA 261Stop — call an engineerAn ignition fault that Worcester define two ways: on the Greenstar i it points at the heat control module, on the Compact range it means the flame was not established inside the four-second ignition window.Related: ignition and gas supply
Own a Worcester Bosch boiler? Save it and its codes come first next time.
Related guides
Common questions about Worcester Bosch EA 234
Is it safe to leave the boiler switched on?
Yes. With 234 the boiler has refused to start because it cannot operate the valve, and no gas has been released. It will sit locked out until it is fixed. If you can smell gas that is a different matter — turn off at the meter and call 0800 111 999.
Will it need a new gas valve?
Often not. A connector that has worked loose is the most common finding, and a coil that has genuinely failed is confirmed with a resistance reading before the valve is condemned. If it has failed, the valve is replaced complete rather than repaired.
Does this code appear on the Greenstar i?
Not as 234. Worcester's Greenstar i table publishes the equivalent as F0 238, gas valve or control box error, with the engineer checking for 230 V across the blue and orange wires to the coils.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.