Baxi H.02-.03 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi H.02-.03 fault code mean?
The Baxi H.02.03 fault code indicates a temporary configuration error on the boiler's printed circuit board (PCB). Specifically, the control board's C1/C2 (also referred to as CN1/CN2) setup parameters have either not been entered, have been entered incorrectly, or have become corrupted. The boiler cannot operate safely without these settings, as they tell the PCB exactly how it has been configured for your particular system. This type of error most commonly surfaces shortly after a new boiler is installed, after a PCB has been replaced, or occasionally following a power surge. It is a PCB-level setup fault that requires a Gas Safe registered engineer to resolve — there is no homeowner fix beyond attempting a single reset.
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
- PCB not commissioned after installation or replacement Common
The most frequent trigger for H.02.03 is a boiler or PCB that has never been fully commissioned. When a new boiler is first installed, or when the PCB is swapped out, the installer must log into the commissioning menu and enter the correct C1/C2 configuration parameters for the specific model and system type. If this step is skipped or interrupted, the boiler will display H.02.03 immediately or shortly afterwards.
- Corrupted configuration settings Sometimes
Even on a correctly commissioned boiler, the stored C1/C2 parameters can occasionally become corrupted. A significant power surge, an unexpected power cut mid-cycle, or a voltage spike on the mains supply can wipe or scramble the PCB's non-volatile memory, causing the board to lose its programmed settings and throw this fault code.
- Faulty PCB unable to retain settings Rare
If the PCB itself has developed a hardware fault — for example a damaged memory chip or a failed component on the board — it may be incapable of storing the configuration parameters even after a successful reconfiguration attempt. In this situation the fault code will return shortly after the engineer re-enters the settings, indicating the board needs repairing or replacing entirely.
How to fix it
- Attempt a single boiler reset DIY safe
Locate the reset button on the front panel of your Baxi boiler. Press and hold it for approximately 3 seconds until the boiler attempts to restart. If the H.02.03 code clears and the boiler fires up normally, monitor it over the next few hours. If the code returns, do not keep resetting — move on to the next step. Repeated resets will not fix an underlying configuration fault.
- Check for a recent power cut or power surge DIY safe
Think back to whether there has been a power cut, a tripped circuit breaker, or a noticeable power surge in the home around the time the fault appeared. If so, note this down and mention it when you speak to an engineer — it helps confirm whether this is a one-off corruption event or a recurring hardware fault. There is nothing further a homeowner can safely do at this stage.
- Do not attempt to access the installer or commissioning menu Gas Safe engineer
Some Baxi models allow access to an installer menu via a key combination or PIN. Entering incorrect parameters here can cause further faults or leave the boiler in an unsafe state. This area of the boiler is strictly for Gas Safe registered engineers with the correct Baxi technical documentation. Do not attempt this yourself.
- Call a Gas Safe registered engineer to reconfigure the PCB Gas Safe engineer
A Gas Safe engineer will access the boiler's installer commissioning menu and re-enter the correct C1/C2 (CN1/CN2) parameters for your boiler model and system configuration. They may need to refer to Baxi's technical portal (baxiworks.co.uk) for the specific parameter values. Once the settings are saved, they will reset and test the boiler to confirm the fault has cleared. This is typically a straightforward job taking under an hour on site.
- If the fault returns after reconfiguration, the PCB may need replacing Gas Safe engineer
Should the H.02.03 code reappear shortly after a successful reconfiguration, the PCB is likely unable to retain its settings due to a hardware fault. Your engineer will advise whether the board can be repaired or whether a full PCB replacement is more cost-effective. On boilers over 8–10 years old, it is worth comparing the PCB replacement cost against the price of a new boiler installation, as they can be similar in value.
Parts you may need
- Baxi PCB (printed circuit board) · from £280
- PCB configuration / commissioning service (labour) · from £100
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 £80–£350, depending on the underlying cause.
Frequently asked questions
Can I fix Baxi H.02.03 myself by resetting the boiler?
You can try a single reset — press and hold the reset button on the front panel for about 3 seconds. If the code disappears and the boiler runs normally, keep an eye on it. However, if H.02.03 returns, a reset will not solve the underlying problem. The C1/C2 configuration parameters need to be re-entered through the installer commissioning menu, which requires a Gas Safe registered engineer with access to Baxi's technical documentation. Attempting to access the installer menu yourself risks making the fault worse.
Why has H.02.03 appeared on a brand new Baxi boiler?
This is actually one of the most common situations for H.02.03. If the installer did not fully complete the commissioning process — including entering the correct C1/C2 parameters for your specific system — the PCB will flag this fault straight away. Contact your installer or Baxi's customer support line. If the boiler was installed recently, this should be rectified under the installation warranty at no extra cost to you.
How much does it cost to fix Baxi H.02.03?
If the fix is simply reconfiguring the PCB settings, you are mainly paying for engineer call-out and labour — typically £80 to £150 in total for a standard visit. If the PCB has a hardware fault and cannot hold its settings, a full PCB replacement is needed, which usually costs £300 to £600 including parts and labour in the UK. On older boilers, always ask your engineer to compare the repair cost against the cost of a new boiler before committing.
Will H.02.03 damage my Baxi boiler if I leave it?
The boiler will not run while this fault is active, so there is no risk of ongoing damage from continued operation. However, leaving your home without heating or hot water for an extended period is obviously inconvenient, and on very cold days a lack of heating can lead to frozen pipes. Get the fault looked at promptly — it is usually a quick fix if it is simply a commissioning oversight rather than a faulty PCB.