Baxi E.04-.17 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E.04-.17 fault code mean?
The E.04-.17 code is a permanent lockout fault on Baxi boilers, triggered when the boiler's control system detects a problem with the gas valve or the gas-air unit (sometimes called the venturi assembly). Because the boiler cannot verify safe gas control, it shuts down completely and will not restart by itself — a simple reset alone will not clear this fault unless the underlying cause is first resolved. The code specifically points to an electrical or mechanical failure in the gas valve control circuit, meaning the component responsible for regulating how gas reaches the burner is either not responding correctly or has failed outright.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or failed gas valve Common
The gas valve controls how much gas enters the burner. If it fails electrically or mechanically, the boiler's PCB cannot confirm safe operation and triggers the permanent lockout. This is the most frequently diagnosed root cause of E.04-.17.
- Electrical fault in the gas valve control circuit Common
Even if the valve itself is physically intact, a break or short in the wiring between the PCB and the gas valve can produce exactly this fault. Corroded terminals, chafed cables, or a loose plug are typical culprits.
- Defective gas-air (venturi) unit Sometimes
The gas-air ratio unit mixes gas and air in the correct proportions before combustion. If this assembly fails or becomes blocked, the boiler cannot achieve safe ignition and locks out. An engineer will check this if the valve and wiring prove sound.
- PCB control circuit failure Sometimes
If the PCB's output driver for the gas valve is damaged, it will be unable to open or monitor the valve correctly, producing this fault even when the valve and wiring are otherwise fine.
- Frozen condensate pipe (winter only) Sometimes
In sub-zero conditions, the plastic condensate pipe that runs outside can freeze solid, blocking drainage and preventing the boiler from firing. Although this does not directly damage the gas valve, it can be the trigger that causes a lockout in winter. It is worth ruling out before calling an engineer.
- Interrupted or low gas supply Rare
If gas pressure at the meter is unusually low, or supply has been interrupted, the boiler may lock out before the valve has a chance to open properly. Checking other gas appliances is a quick first step.
How to fix it
- Check your gas supply is on and working DIY safe
Try another gas appliance such as a hob or gas fire. If nothing is working, contact your gas supplier — there may be a street-level supply issue. If you are on a prepayment meter, make sure you have credit.
- Look for a frozen condensate pipe in cold weather DIY safe
The condensate pipe is typically a white or grey plastic pipe (21–32 mm diameter) that exits the boiler and runs to an outside drain. If the weather has been below freezing, feel along its length for a solid blockage. You can gently thaw it by pouring warm (not boiling) water over the frozen section, working from the drain end back towards the boiler. Once clear, attempt a reset.
- Attempt a single boiler reset DIY safe
Press and hold the reset button on your Baxi boiler (usually marked with a flame or reset symbol) for around 3 seconds. Only try this once or twice — if the E.04-.17 code returns immediately, do not keep resetting. Repeated resets will not fix a permanent fault and may mask the underlying problem.
- Check that air vents and the flue terminal are unobstructed DIY safe
Make sure nothing is blocking the external flue terminal (e.g. a bird's nest, debris, or snow). Also check that furniture or storage has not been placed directly in front of the boiler, covering ventilation openings. Do not attempt to access the flue pipe itself.
- Call a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
Because E.04-.17 is a permanent lockout relating to gas valve or gas-air unit control, any further investigation must be carried out by a Gas Safe registered engineer. They will connect a fault-code reader, inspect wiring connections and terminals to the gas valve and PCB, and test component operation safely.
- Engineer to inspect and test the gas valve wiring harness Gas Safe engineer
The engineer will check every connection between the PCB and the gas valve for loose plugs, corrosion, or damaged insulation. A wiring fault is often the quickest and least expensive fix, and should be ruled out before replacing more expensive components.
- Engineer to test or replace the gas valve Gas Safe engineer
If wiring is sound, the engineer will test the gas valve's electrical coils and mechanical operation. A failed valve must be replaced with a genuine Baxi-compatible part. This work involves disconnecting the gas supply and must only ever be performed by a Gas Safe registered engineer.
- Engineer to inspect the gas-air ratio (venturi) unit Gas Safe engineer
If the valve passes testing, attention turns to the venturi assembly. The engineer will check for blockages, damage, or calibration drift that could cause incorrect gas-air mixing and trigger the lockout.
- Engineer to test or replace the PCB if required Gas Safe engineer
Should the gas valve and venturi both be confirmed as functioning correctly, the PCB's output circuit for gas valve control may be at fault. PCB replacement is a last resort and should only follow thorough component testing to confirm the diagnosis.
Parts you may need
- Baxi gas valve assembly · from £95
- Gas valve wiring harness / loom · from £35
- Gas-air ratio (venturi) unit · from £75
- Baxi PCB (printed circuit board) · from £160
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£380, depending on the underlying cause.
Frequently asked questions
Can I reset a Baxi E.04-.17 fault myself and will it clear it?
You can attempt one or two resets, and occasionally a one-off glitch (such as a brief gas supply interruption) may not return. However, E.04-.17 is classed as a permanent lockout, meaning the boiler's safety system has detected a genuine fault and will keep locking out until the underlying cause is repaired. Repeatedly resetting without fixing the root problem is not recommended and will not resolve a faulty gas valve or damaged wiring.
How much does it cost to fix a Baxi E.04-.17 fault in the UK?
For most people, the total repair bill — parts and labour — falls between £150 and £380. A wiring repair sits at the lower end (roughly £100–£180 in labour), while a gas valve replacement typically runs to £180–£300 all-in. If the PCB needs replacing, costs can rise to £300–£450 depending on the model. If your boiler is over 10 years old and has needed several repairs recently, it may be worth getting a new boiler quote alongside the repair estimate, as a modern replacement could work out more cost-effective in the long run.
Is a Baxi E.04-.17 fault dangerous?
The boiler has locked out as a deliberate safety measure — it has detected that it cannot control the gas valve safely and has shut itself down rather than risk a hazardous situation. Do not attempt to bypass the lockout or tamper with any gas components. Leave the boiler off and call a Gas Safe registered engineer. The fault itself is not immediately dangerous precisely because the boiler has stopped operating.
How long does it take to repair a Baxi E.04-.17 fault?
In most cases an experienced engineer can diagnose and repair this fault in a single visit of one to two hours. A wiring or connection fix is typically the quickest outcome. Gas valve replacement takes a little longer as the gas supply must be isolated, the component swapped, and the system re-commissioned and tested. PCB replacement is similar in time. Your engineer should be able to give you a realistic timeframe and a fixed quote before starting any work.