Remeha H.02.03 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha H.02.03 fault code mean?
H.02.03 is a temporary blocking fault (the 'H' prefix indicates the boiler has paused rather than permanently locked out) triggered when the boiler's control unit cannot recognise or read its own configuration settings. Specifically, the two configuration parameters known as CN1 and CN2 — which tell the control board exactly what appliance it is running on — are either missing, unrecognised, or have become corrupted. Until these values are correctly entered, the boiler will refuse to fire. This is fundamentally a software/settings issue rather than a mechanical breakdown, which is why the boiler itself may be in perfectly good physical condition yet still display this code.
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 replaced without re-entering configuration codes Common
When a main printed circuit board is fitted as a replacement, the new board arrives without the boiler-specific CN1 and CN2 values pre-programmed. If the engineer who fitted the board did not re-enter these codes from the data plate, H.02.03 will appear immediately or after the next power cycle. This is the single most common trigger for this fault.
- Control unit (CU-GH) replacement without reconfiguration Common
The control unit stores the CN1 and CN2 parameters. Swapping it out — even for an identical unit — wipes those values. The replacement unit needs the configuration numbers re-entered via the installer menu before the boiler will run normally.
- Power cut or hard reset clearing configuration memory Sometimes
An extended power outage, a factory reset performed during servicing, or an unexpected voltage spike can occasionally corrupt or erase the stored configuration parameters. The boiler powers back on but the control board no longer recognises its own settings, producing H.02.03.
- Corrupted parameter list in the control board Rare
In rare cases the parameter memory on the PCB degrades over time or develops a fault, causing the configuration data to become unreadable without any external trigger such as a board swap or reset. This typically points to a failing PCB or CSU (configuration storage unit).
How to fix it
- Note down the fault code and check the boiler display DIY safe
Confirm the display is showing H.02.03 (sometimes displayed as 'Conf Error'). Take a photo of the display for reference. This is a blocking fault, so the boiler will not fire until it is resolved — there is no value in repeatedly pressing reset, as the underlying configuration issue will not clear itself.
- Locate the boiler data plate and find the CN1 and CN2 values DIY safe
The data plate is a label affixed to the boiler casing — often inside the front panel or on the inner side of the casing door. It lists model-specific configuration numbers including CN1 and CN2. Write these down and have them ready for the engineer; this will save time and potentially reduce the call-out cost.
- Do not attempt to access the installer menu yourself Gas Safe engineer
Re-entering CN1 and CN2 requires navigating the boiler's password-protected installer/service menu. Entering incorrect values can cause further faults or unsafe operation. This task must only be carried out by a qualified heating engineer — it is not a homeowner-accessible setting.
- Arrange for a Gas Safe registered engineer to re-enter the CN1 and CN2 configuration codes Gas Safe engineer
The engineer will access the installer menu, input the CN1 and CN2 values from the data plate, then restart the boiler to verify the fault clears. In straightforward cases — such as after a PCB swap where the values were simply not entered — this resolves the fault entirely with no parts required.
- If reconfiguration does not clear the fault, the engineer should inspect the CSU and PCB Gas Safe engineer
If the control board cannot retain or read the configuration even after correct values are entered, either the CSU (configuration storage unit — a smaller plug-in memory component) or the main PCB itself may be faulty. The engineer will advise on replacement. Always ask for a written quote before authorising parts work.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
H.02.03 will not resolve without installer-level intervention. Contact a Gas Safe registered engineer or Remeha's own technical support line (0330 678 0140) to arrange a visit. Confirm the engineer has experience with Remeha appliances, as familiarity with the installer menu speeds up the job considerably.
Parts you may need
- Remeha main PCB (printed circuit board) · from £280
- Remeha CSU (configuration storage unit) · from £95
- Remeha control unit CU-GH · from £220
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 £100–£380, depending on the underlying cause.
Frequently asked questions
Can I fix Remeha H.02.03 myself by resetting the boiler?
Unfortunately not. A standard boiler reset will not clear H.02.03 because the fault is caused by missing or unrecognised configuration parameters (CN1 and CN2) in the control board — not a temporary sensor glitch or ignition hiccup. The only way to clear it is to re-enter the correct CN1 and CN2 values via the installer menu, which is password-protected and intended for qualified engineers only. Repeatedly pressing reset will not help and may mask the fault temporarily before it returns.
Why has H.02.03 appeared after my boiler was serviced or repaired?
This is the most common scenario. If the engineer replaced the PCB or control unit during that visit and did not re-enter the CN1 and CN2 configuration codes from the boiler's data plate, H.02.03 will appear as soon as the boiler restarts. Contact the engineer who carried out the work — rectifying a missing configuration entry after a board swap should be a quick job and, depending on your agreement, may be covered under the original repair.
What are CN1 and CN2 on a Remeha boiler?
CN1 and CN2 are two numerical codes specific to each Remeha appliance model and variant. They tell the control board exactly what type of boiler it is installed in — including heat output, gas type, and other model-specific parameters. Without these values the board cannot safely operate the burner. The correct numbers for your particular appliance are printed on the data plate, which is usually found inside the boiler casing. Note them down before calling an engineer, as having them to hand speeds up the repair.
How much does it cost to fix Remeha H.02.03 in the UK?
If the fault is simply down to missing configuration codes after a board swap or reset, most engineers will resolve it for £100–£150, covering their call-out and the time to access the installer menu. If the CSU (configuration storage unit) needs replacing, expect to pay around £150–£300 including parts and labour. A full PCB replacement is more expensive — typically £320–£500 or more once parts and labour are included — though this is only necessary if the board itself is found to be faulty. Prices vary by region and engineer, so always ask for a quote upfront.