Error H.02 – .04

Safety precautions:

1) If you smell gas, immediately turn off the gas supply at the meter if safe to do so, evacuate the property and call the gas emergency number. Do not operate electrical switches or the boiler.

2) Before opening the boiler cover or touching internal wiring, switch off electrical power to the boiler at the isolator or fuse and wait a few minutes. Only proceed if you are competent and confident; otherwise call a Gas Safe engineer.

3) Never attempt to adjust gas valves, set ignition timing, or change installer parameters unless you are a qualified engineer.

Initial checks a homeowner can do:

1) Note the exact error code and any other codes or lights shown on the display. Write down what appears and when it started.

2) Check boiler pressure on the gauge; ensure it is within the normal range (typically about 1.0–1.5 bar when cold for combi boilers). If pressure is very low (below 0.5 bar) top up using the filling loop per your manual, then retry.

3) Perform a basic reset: locate the boiler reset button (or selector to R) and press/hold for about 5–10 seconds to let the boiler attempt a restart. Alternatively, switch the boiler off at the isolator, leave for 60 seconds and switch back on.

4) After reset, try calling for heating and hot water and observe if H.02 – .04 returns. Do not keep trying resets repeatedly more than 2–3 times.

If the fault persists after reset and basic checks:

1) Check for obvious signs of trouble visible externally: water leaks near the boiler, recent power surges or lightning, signs of corrosion, or rodent damage to cables.

2) If you are competent and have isolated electrical power: remove the outer cover to visually inspect wiring connections to the main PCB and HMI (display) cable for loose connectors, burn marks or corrosion. Do not touch or re-seat components unless you are experienced. If you do re-seat connectors, ensure power is off and reconnect firmly.

3) Check that any external control or thermostat connections are properly connected (e.g., room stat or programmer) and that no external control is forcing odd parameters.

4) If the boiler was recently serviced or had settings changed by an installer, inform the engineer as the fault may be caused by incorrect parameter programming (C1/C2).

When to call a professional:

1) If H.02 – .04 returns after a reset, or it repeats intermittently, contact a Gas Safe registered engineer or Baxi support. Persistent parameter faults usually require diagnostic tools, access to service menus, and possibly reprogramming or replacement of the PCB by a qualified engineer.

2) Call immediately if you detect any gas smell, water leak, overheating, or other safety symptoms. Also call an engineer if you are unsure about opening the boiler or handling electrical connections.

What an engineer will likely do:

1) Read full fault history with diagnostic tools and check parameter settings (C1/C2).

2) Check communications between HMI, PCB and gas valve, inspect wiring and connectors and test PCB health.

3) Reconfigure or restore correct parameters, or replace/reprogram the PCB if corrupted or faulty. They will also check for any underlying causes that may have changed parameters (power surges, failed component, water damage).

Final notes:

1) H.02 – .04 can be a transient issue cleared by reset, but repeated or persistent occurrences mean professional attention is required. 2) Avoid repeated resets — if the error reappears after one or two resets, stop and call a qualified engineer.