Baxi H.02-.06 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi H.02-.06 fault code mean?
The H.02 fault code on Baxi boilers is a blocking (temporary) fault, meaning the boiler pauses operation to protect itself but may resume automatically once the underlying condition clears. The H prefix always indicates this self-protective, potentially self-recovering behaviour. There are five distinct sub-codes: H.02.02 means the PCB has not been configured — typically after a board replacement where setup was not completed. H.02.03 points to incorrect configuration settings (CN1/CN2 jumpers or parameters entered wrongly during installation or servicing). H.02.04 flags a parameter error where the settings stored in PCB memory cannot be read or are corrupt. H.02.05 means the memory settings on the board are incompatible with the boiler model — often caused by fitting the wrong replacement PCB or mismatched firmware. H.02.06 is by far the most common sub-code and indicates low system water pressure, a water leak on the boiler itself, or a leak elsewhere in the heating system. On older Baxi models the same pressure issue may have appeared as E10 or E119; H.02.06 is the modern equivalent.
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
- Low system water pressure (H.02.06) Common
The most frequently seen sub-code. System pressure has dropped below the boiler's minimum threshold — typically below 1.0 bar. This can happen after bleeding radiators, a small leak developing on a radiator valve or pipe joint, or simply through natural pressure loss over time. The boiler shuts down to prevent running dry.
- PCB not configured after replacement (H.02.02) Sometimes
A replacement PCB was fitted but the installer did not complete the configuration step — entering the CN1/CN2 parameters required to match the board to the specific boiler model. The boiler cannot operate correctly without these settings being input.
- Incorrect configuration settings (H.02.03) Sometimes
The wrong configuration jumper settings or parameter values have been applied, either during initial installation or after a service. The boiler detects the mismatch and blocks operation.
- Corrupt or unreadable PCB memory (H.02.04) Sometimes
The parameter storage unit on the PCB holds calibration and configuration data. If this memory becomes corrupted — sometimes due to a power surge or component age — the boiler cannot read the settings it needs and raises a blocking fault.
- Incompatible replacement PCB (H.02.05) Rare
A PCB intended for a different Baxi model or carrying different firmware has been installed. The board's stored memory settings do not match what this boiler expects, triggering the blocking fault.
- Leak or faulty pressure sensor (H.02.06 persistent) Sometimes
If pressure drops repeatedly after topping up, there is an active water leak somewhere in the system — possibly at a radiator valve, pipe joint, or on the boiler's internal components. A faulty pressure sensor can also report incorrect readings, or a waterlogged expansion vessel may cause pressure to fluctuate.
How to fix it
- Note the full sub-code displayed DIY safe
Check the boiler display carefully and write down the complete code — H.02.02, H.02.03, H.02.04, H.02.05, or H.02.06. This determines whether the fault is pressure-related (H.02.06, which you can investigate yourself) or PCB/parameter-related (H.02.02–.05, which requires an engineer).
- For H.02.06 — check the pressure gauge DIY safe
Look at the pressure gauge on the boiler front panel. Healthy operating pressure sits between 1.0 and 1.5 bar. If the needle is below 1.0 bar or in the red zone, low pressure is the likely cause and you can attempt to repressurise the system yourself.
- For H.02.06 — repressurise via the filling loop DIY safe
Switch the boiler off and allow it to cool. Locate the filling loop — usually a flexible silver or braided hose with a valve at each end, connecting the cold mains to the heating system (often under the boiler). Slowly open both valves and watch the pressure gauge rise. Stop and close both valves once the gauge reads approximately 1.0–1.5 bar. Do not overfill past 2.0 bar.
- Reset the boiler DIY safe
Press and hold the reset button (usually marked with a flame or reset symbol) for 3–5 seconds. The boiler should attempt to restart. Only reset 2–3 times at most — repeated resets without resolving the underlying fault can cause further damage.
- Check for visible water leaks around the boiler and radiators DIY safe
Inspect the area around the boiler casing, visible pipework, and radiator valves for drips, damp patches, or limescale staining (a sign of a historical slow leak). If you find a leak, do not continue topping up — contact a plumber or Gas Safe engineer to repair it.
- Monitor pressure over the following days DIY safe
If the boiler restarts successfully after repressurising, keep an eye on the pressure gauge over the next few days. Pressure dropping again within a short time points to an active leak or a failing expansion vessel — both need professional attention rather than repeated top-ups.
- For H.02.02–.05, or any persistent H.02.06 — call a Gas Safe registered engineer Gas Safe engineer
PCB configuration and parameter faults (H.02.02–.05) cannot be resolved by a homeowner — they require an engineer to reconfigure CN1/CN2 settings, restore PCB parameters, or replace the board with a correctly matched unit. Similarly, if H.02.06 keeps returning after repressurising, an engineer needs to locate the leak, inspect the expansion vessel, and test the pressure sensor. Do not attempt to open the boiler casing or work on any internal components yourself.
Parts you may need
- Baxi replacement PCB · from £250
- Pressure sensor · from £35
- Expansion vessel · from £55
- Filling loop assembly · from £20
- Pressure relief valve · from £18
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 £120–£380, depending on the underlying cause.
Frequently asked questions
Can I fix a Baxi H.02.06 fault myself?
In many cases, yes. If the fault is simply low system pressure, you can repressurise the boiler yourself using the filling loop at no cost. Top up to around 1.0–1.5 bar, reset the boiler, and it should fire up again. However, if the pressure keeps dropping — say, within days of topping up — that points to an active leak or a failing expansion vessel, and you should call a Gas Safe engineer rather than keep refilling.
What is the difference between H.02.02, H.02.03, H.02.04, and H.02.05?
All four are PCB or configuration-related blocking faults. H.02.02 means the board has never been configured after fitting. H.02.03 means the configuration settings entered are wrong. H.02.04 means the parameters stored in the PCB memory are corrupt or unreadable. H.02.05 means the board itself is incompatible with the boiler model. None of these are homeowner-fixable — they all need a Gas Safe engineer to reconfigure settings or supply and fit a correctly matched PCB.
How much does it cost to fix a Baxi H.02 fault in the UK?
For H.02.06 caused purely by low pressure, repressurising yourself costs nothing. If an engineer attends, it is usually covered within a standard call-out fee of around £65–£90. For PCB-related faults (H.02.02–.05), expect to pay £200–£380 in total once parts and labour are combined. PCBs alone typically cost £200–£300 for the part; in rare cases where the boiler is older and the correct board is hard to source, costs can climb higher — worth discussing with your engineer before proceeding.
My Baxi boiler used to show E10 or E119 for low pressure — is H.02.06 the same thing?
Yes, effectively. Older Baxi models used E10 or E119 to flag low system water pressure. Newer Baxi boilers display the same underlying condition as H.02.06. The cause, the checks, and the fix are all the same — check the pressure gauge, repressurise if needed, and investigate any recurring pressure loss.