Overview
H.02 – .03 on a Baxi 200/400 combi means the boiler has detected a configuration/parameter problem with the PCB (the control board) — specifically the C1/C2 configuration parameters are incorrect or missing. C1/C2 are installer/programming parameters that tell the boiler how to behave with respect to system type, external controls and certain operating options. This is usually reported as a temporary fault because the boiler can sometimes clear it after a reset, but it can reappear if the parameters remain wrong or the PCB/software has become corrupted. Severity is generally low-to-medium: the boiler will often lock out or go into a safe mode until the configuration is correct, so you may lose heating or hot water until the issue is resolved. Because the cause is related to internal configuration, firmware or wiring to control modules, most corrective actions require a qualified Gas Safe engineer or an installer with the correct service tools. Homeowners can perform a few safe checks and a reset, but should not attempt to reconfigure the PCB or work on gas connections themselves.
Possible Cause: Temporary error- incorrect configuration settings C1/C2.
Troubleshooting Steps
Safety first
1) If you smell gas anywhere: leave the property immediately, do not operate electrical switches, and call your gas emergency number / the emergency services. Do not try to repair the boiler yourself.
2) If you see signs of water leaking or significant damage, isolate the electrical supply to the boiler at the fused spur and call a qualified engineer.
3) Do not open the boiler casing or attempt internal PCB adjustments unless you are a Gas Safe registered engineer.
Initial checks you can safely do at home
1) Note the exact error code and any extra digits or messages on the display and the time it appeared. Take a photo for the engineer.
2) Check the boiler pressure gauge — aim for around 1.0–1.5 bar when cold. If pressure is very low (below about 0.5–0.7 bar) follow your manual to repressurise using the filling loop; low pressure can cause other faults. If unsure, stop and call a professional.
3) Check recent changes: has the boiler had power cuts, been worked on, had its PCB or wiring altered, or had new thermostats or wireless controls fitted? New or replaced parts and lost power are common triggers for parameter/configuration faults.
4) Inspect visible external wiring to thermostats, programmers and wireless receivers for obvious damage or loose connectors (do not remove covers or touch live terminals).
Reset and simple diagnostic steps
1) Try a normal reset: on many Baxi combi models press and hold the reset button or set the selector to R and hold for 5–10 seconds (refer to your boiler manual for the exact reset method for your model). Wait for the boiler to attempt restart and watch the display.
2) If a reset does not work, switch the boiler off at the programmer and at the isolator or fused spur, wait 60 seconds, then restore power and attempt a reset again.
3) After reset, observe whether the H.02 error clears and whether the boiler returns to normal operation. If it clears and does not return, monitor for recurrence but avoid repeated resets if the fault returns immediately.
4) Try isolating external controls temporarily: set the room thermostat and programmer to request heat (e.g., turn up the thermostat and put programmer in a permanent call for heat) to check whether the boiler responds without external control interference. If you have a wireless thermostat, ensure its receiver is powered and paired — unpaired or failed external controls can cause configuration/communication issues.
When to call a professional and what to tell them
1) If the H.02 – .03 persists after resets and basic checks, contact a Gas Safe registered heating engineer. This fault indicates parameter/PCB configuration issues that usually require service tools and access to the boiler’s installer menus to inspect or reload C1/C2 parameters, update firmware or repair/replace a faulty control board.
2) Do not keep resetting the boiler repeatedly — this can mask the underlying problem and may stress components.
3) When you call the engineer give them: the exact fault code (H.02 – .03), when it started, whether the boiler was power-cycled, any recent work or replacements, photos of the display and the pressure gauge reading. Mention any external controls added or changed recently.
Why a professional is usually needed
1) Correcting C1/C2 means accessing installer/service settings, verifying correct parameter values for your exact boiler configuration and possibly reprogramming or replacing the PCB or PU. Only a qualified Gas Safe engineer should perform those tasks to ensure safe gas combustion and compliance with regulations.
2) If the fault stems from a damaged PCB, communication fault between modules, or failed components, a trained engineer can diagnose with the manufacturer service tools and replace parts safely.
Final note
This error is often temporary and may clear with a reset, but persistent appearance indicates a configuration, communication or PCB problem that needs professional attention. Avoid DIY internal repairs, do not work on gas or live electrical components, and call a Gas Safe registered engineer if the fault does not reliably clear after the simple, safe steps above.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi 200 / 400 Combi Gas Boiler.