Buderus 9P 239 Fault Code: Causes, Fixes & Repair Costs
What does the Buderus 9P 239 fault code mean?
The 9P fault code (display value 239) appears on Buderus boilers when the main controller cannot successfully read or communicate with the KIM — the Key Identification Module. The KIM is a small EEPROM-based identification chip that sits on the DBA control panel circuit board. It holds configuration data the boiler needs to operate correctly, so if it cannot be detected — whether due to a loose connection, a short circuit at its contacts, or a defective control board — the boiler locks out and displays 9P. In short, the boiler's brain cannot recognise its identity chip, and it refuses to run until the issue is resolved.
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
- KIM module loose or incorrectly seated Common
The KIM chip must be firmly and correctly pushed into its connector on the DBA board. Vibration during transit, a previous service, or simple wear can cause it to work loose, breaking the electrical contact the controller needs. This is the first thing any engineer will check, as it is the most common root cause and the cheapest to resolve.
- Faulty or failed DBA control board (PCB) Common
If the KIM itself tests fine but the error persists, the DBA control board may no longer be capable of reading the module. Signs of a failing board include visible deformation, burnt or discoloured components, damaged tracks, failed capacitors, or traces of moisture ingress. A failed board requires professional diagnosis and replacement.
- Electrical supply problems — incorrect voltage or poor earthing Sometimes
The boiler's electronics expect a stable 230V ±10% supply with a solid earth connection. A weak or absent earth can cause intermittent 9P faults that come and go unpredictably. Similarly, an undersized or faulty consumer unit connection can produce voltage dips that upset the KIM recognition process.
- New control board installed with incorrect configuration Sometimes
If a PCB has recently been replaced, a 9P fault can appear if the replacement board has not been correctly configured or matched to the specific boiler model. The board parameters must correspond exactly to the boiler variant — an incorrectly programmed replacement will not recognise the KIM even if the module itself is undamaged.
- Electrical interference or stray currents Rare
External electrical interference — from nearby high-current equipment, damaged cable insulation, or proximity to power lines — can disrupt the signal between the controller and the KIM. This tends to produce intermittent rather than permanent faults and is more likely in older installations with ageing wiring.
How to fix it
- Switch the boiler off at the power switch and wait 30 seconds, then switch it back on DIY safe
A temporary power interruption can sometimes clear a transient communication glitch between the controller and the KIM. This is the quickest first step. If the 9P code disappears and does not return, monitor the boiler over the next few days.
- Attempt a boiler reset — but no more than two or three times DIY safe
On most Buderus models there is a Reset button on the front panel. Press and hold it for approximately five seconds. Do not reset more than two or three times in succession — repeated resets when the burner will not start can damage the ignition transformer. If the fault returns immediately or will not clear, stop resetting and move on.
- Check that the gas supply to the boiler is turned on and other gas appliances in the property work DIY safe
While 9P is not a gas-pressure fault, it is worth ruling out a general supply interruption before calling an engineer. Check whether your gas hob or other appliances light normally. If there is no gas supply, contact your gas supplier.
- Have a Gas Safe engineer inspect and reseat the KIM module Gas Safe engineer
The KIM sits on the DBA board inside the boiler casing. An engineer will isolate the boiler from the mains, open the casing, and carefully reseat the KIM in its connector, ensuring it is fully and correctly engaged. This alone resolves many 9P faults at minimal cost. If reseating clears the code, the engineer will run functional checks before leaving.
- If reseating does not resolve the fault, have the KIM module tested and replaced if necessary Gas Safe engineer
The engineer can test the KIM independently. If it has failed — which can happen due to age, moisture, or an electrical spike — a replacement KIM is the next step. This is a relatively low-cost component compared to a full board replacement and should always be tried before condemning the PCB.
- Have the DBA control board (PCB) inspected and replaced if found to be defective Gas Safe engineer
If the KIM is confirmed good but the 9P fault persists, the DBA control board itself is likely defective. The engineer will check for visible damage such as burnt tracks, failed components, or moisture. If the board is beyond repair, a replacement board will need to be sourced, fitted, and correctly configured for your specific boiler model. PCB work involves connections to the gas valve and safety controls and must only be carried out by a Gas Safe registered engineer.
- Ask your engineer to verify the mains voltage and earthing at the boiler Gas Safe engineer
If neither the KIM nor the PCB is found to be obviously damaged, intermittent 9P faults may point to an electrical supply problem. The engineer can check incoming voltage and confirm the earth connection is solid, which may require liaison with a qualified electrician if the consumer unit or building wiring is at fault.
- Contact a Gas Safe registered engineer if you have not already done so Gas Safe engineer
If the steps above have not resolved the fault, or if you are unsure about any aspect of the diagnosis, book a Gas Safe registered Buderus specialist. They will have access to manufacturer diagnostic tools and the correct replacement parts. You can find Gas Safe registered engineers at the official Gas Safe Register website (gassaferegister.co.uk).
Parts you may need
- Buderus KIM (Key Identification Module) · from £45
- Buderus DBA Control Board (PCB) · from £320
- PCB specialist repair service (board refurbishment) · 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 £120–£450, depending on the underlying cause.
Frequently asked questions
Can I fix the Buderus 9P fault myself?
The only safe DIY steps are switching the boiler off and on, attempting a reset (no more than two or three times), and checking your gas supply is on. Everything else — opening the boiler casing, reseating or replacing the KIM, or inspecting the PCB — must be done by a Gas Safe registered engineer. The control board is connected to the gas valve and safety systems, and working on it without Gas Safe registration is both illegal and dangerous.
How much does it cost to fix a Buderus 9P fault in the UK?
If the KIM simply needs reseating, you may only pay the engineer's callout and labour charge — typically £80 to £150 depending on your region. A KIM replacement adds around £45 in parts. If the full DBA control board needs replacing, expect to pay £300 to £450 all-in for parts and labour, though costs can be higher in London and the South East. A specialist PCB repair service is worth considering for boards that show physical damage — these typically charge £80 to £120 and often provide a 12-month warranty on the repair.
Is it worth replacing the PCB on an older Buderus boiler?
If your boiler is under eight years old and otherwise in good condition, a PCB replacement is generally a sensible repair. On a boiler that is ten years old or more, especially one that has had other component failures, it is worth weighing the repair cost (£300–£450 or more) against the cost of a new installation. A new combi boiler typically costs £1,800–£3,000 installed, so on an ageing boiler the sums can sometimes favour replacement — particularly when you factor in improved efficiency and a fresh warranty.
What is the KIM module on a Buderus boiler?
KIM stands for Key Identification Module. It is a small EEPROM chip mounted on the DBA control panel board inside the boiler. It stores identification and configuration data that the main controller needs in order to recognise the boiler's specification and operate safely. Without a working KIM that the controller can read, the boiler will lock out and display the 9P fault code. It is a relatively inexpensive component, so an engineer will always try replacing just the KIM before moving on to replacing the entire control board.