If your Baxi boiler is showing E430 or 166, Baxi’s current error-code table describes it as a water pressure temporary fault. The boiler has detected a pressure-related condition that prevents it from operating normally at that moment.
You may also see E430 / 166 with a crossed-flame symbol. Baxi gives that version a different description: water pressure test failed. The number is similar, but the extra display symbol is important, so take a clear photo of the whole display if you can.
What does Baxi E430 / 166 mean?
A sealed central-heating system needs the correct water pressure for the boiler to circulate heat safely. E430 / 166 means the boiler has detected a temporary water-pressure fault. The code does not prove that the visible gauge is low, and it does not identify a particular component on its own.
Pressure can be affected by water loss from the heating system, trapped air after work, a pressure-reading problem or another condition that needs testing. The engineer must use the code, the model-specific technical information and checks at the appliance to establish what is actually happening.
What is the crossed-flame version?
According to Baxi, plain E430 / 166 means “water pressure temporary fault”. E430 / 166 accompanied by a crossed-flame symbol means “water pressure test failed”. Do not ignore the symbol or treat both displays as identical.
Record the complete display rather than only writing down the number. If the screen alternates between different information, a short photo or video taken from outside the boiler can help the engineer see the sequence. There is no need to remove the casing.
Which Baxi boilers use E430 / 166?
Baxi’s current grouped error-code table associates E430 / 166 with ranges including Platinum Compact, Duo-tec Compact, Megaflo Compact System, Baxi 600 and 800 Combi and System, Duo-tec Combi, Assure Combi and System, Platinum and Platinum+, Megaflo System, and EcoBlue Combi and System boilers.
The controls and normal pressure guidance are not identical across every model. Check the exact model name and use the matching Baxi user guide. Advice for a different boiler may place controls in the wrong position or describe a filling arrangement that your system does not have.
What can you safely check?
Keep the boiler casing closed. You can make a few observations without dismantling or adjusting internal parts:
- Note whether the display shows plain E430 / 166 or includes the crossed-flame symbol.
- Look at the pressure gauge or pressure reading from the normal user position.
- Check for visible water around radiators, accessible pipework or beneath the boiler, without removing covers.
- Think about whether a radiator was recently bled or any heating work was carried out.
- Use the exact user guide to check the normal cold-system pressure for your model.
Do not assume a particular gauge reading is correct for every Baxi boiler. If your user guide clearly includes a homeowner repressurising procedure and you are confident you have identified the correct controls, follow that guide exactly once. Stop if the controls are unclear, the pressure rises rapidly, water appears or the code remains.
Do not turn unfamiliar valves, use a filling device that is not described in your guide, remove the casing, adjust a pressure sensor, enter installer settings or inspect wiring. Repeatedly adding water is not a repair. If the pressure keeps falling, the underlying reason needs attention.
What if the pressure gauge looks normal?
A normal-looking gauge does not cancel the code. The reading you can see may not reflect what the boiler’s controls are detecting, and the crossed-flame version specifically indicates that the boiler’s water-pressure test has failed.
If the code remains after the one safe action permitted by your model’s user guide, or if you are unsure what the display is showing, leave the boiler off and arrange a repair. Tell the engineer whether the gauge moved, whether the fault followed radiator bleeding or other work, and whether heating or hot water stopped at the same time.
When should you stop and get help?
Arrange professional help if E430 / 166 returns, the pressure falls again, the boiler will not restart, you can see water near electrical parts, or you cannot confidently identify the correct user control. If water is actively leaking, keep people away from wet electrical equipment and switch off the relevant supply only if it is safe to reach and operate.
If you smell gas, suspect carbon monoxide or a carbon-monoxide alarm sounds, do not continue checking the boiler. Ventilate the property, leave if necessary and call the National Gas Emergency Service on 0800 111 999 from a safe place. Do not operate electrical switches or use naked flames where gas may be present.
What will help the repair visit?
Have the exact model, full display information and a photo of the gauge ready. Note whether pressure was recently added, whether radiators were bled, whether any leak is visible and how quickly the reading changed. Honest observations are more useful than repeated resets or attempts to recreate the fault.
You can find more safe, plain-English boiler guidance in our boiler help and advice hub.
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