Buderus 9P Fault Code: Causes, Fixes & Repair Costs
What does the Buderus 9P fault code mean?
The 9P fault code appears when the boiler's UBA 3 burner control board is unable to communicate with or identify the KIM (Key Identification Module) during startup. The KIM is a small plug-in chip that holds boiler-specific configuration data; without it, the UBA 3 cannot operate safely, so the boiler locks out and stops providing heating and hot water. On older Buderus 500 and 600 series models (11S, 19S, 24S, 24C) the fault may be described as a DBA control panel defect, but the underlying cause is the same — the control system cannot read its configuration module.
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 incorrectly seated Common
The most frequent trigger. The KIM must be inserted directly into the UBA 3 board before the UBA is mounted to the sub-base. If the UBA is fitted to the sub-base first, the KIM can be pushed too far back and miss the connector entirely, preventing recognition even though it appears to be in place.
- Defective or failed KIM module Common
The KIM chip itself can fail — either through age, a power surge, or physical damage. A faulty KIM will consistently prevent the UBA 3 from starting up, and the fault will return immediately after each reset.
- UBA 3 control board fault Sometimes
If the KIM is confirmed to be correctly seated and the fault persists after a replacement KIM is tried, the UBA 3 board itself may have failed. A blown internal fuse on the UBA 3 can sometimes cause a temporary 9P fault; if the board is more deeply damaged, full replacement is required.
- Electrical supply or earthing problem Sometimes
Mains voltage outside the acceptable range, a missing or high-resistance earth connection, or stray electrical currents in the property's wiring can all interfere with the UBA 3's ability to read the KIM. This cause tends to produce an intermittent 9P fault rather than a permanent one.
- Failed mains transformer Rare
In some real-world cases a failed transformer — either caused by or causing damage to the UBA 3 — has been identified as the root cause. Replacing both the transformer and the UBA 3 resolved the fault permanently.
How to fix it
- Reset the boiler DIY safe
Press and hold the reset button on the boiler's front panel for approximately five seconds. If the boiler fires up normally, monitor it over the next day or two. A one-off 9P after a power cut or surge can sometimes be cleared this way. Do not attempt more than two or three resets if the fault keeps returning.
- Check your mains electricity supply DIY safe
Confirm the boiler's isolator switch is on and that the relevant circuit breaker in your consumer unit has not tripped. If other appliances on the same circuit are also behaving oddly, contact an electrician — an unstable supply can cause intermittent 9P faults.
- Contact a Gas Safe registered engineer to reseat the KIM Gas Safe engineer
A qualified engineer will power down the boiler, remove the UBA 3 from its sub-base, and reinsert the KIM directly and firmly into the UBA 3 connector before remounting the assembly. This is the correct factory-specified method and often resolves the fault without any parts being needed.
- Engineer to test and replace the KIM module if necessary Gas Safe engineer
If reseating the KIM does not clear the 9P code, the engineer will fit a new KIM module. These are boiler-specific, so a genuine Buderus part must be sourced. The boiler is then powered up to confirm the UBA 3 recognises the new module.
- Engineer to inspect and replace the UBA 3 control board Gas Safe engineer
Should the fault persist after a new KIM is fitted, the UBA 3 board itself is likely defective. The engineer will check for a blown fuse on the board first; if the board is beyond repair, a replacement UBA 3 will be fitted and the new KIM programmed to it. On some cases the mains transformer is checked and replaced at the same time.
- Engineer to carry out a full electrical and earthing check Gas Safe engineer
If 9P faults are recurring despite a good KIM and UBA 3, the engineer should verify the mains voltage is within the correct tolerance and that the boiler's earth connection is sound. Stray currents or a missing earth can cause ongoing issues that damage replacement parts prematurely.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
All of the diagnostic and repair work beyond a simple boiler reset requires a qualified engineer with access to Buderus-specific diagnostic tools and genuine parts. Buderus is a specialist brand, so it is worth requesting an engineer with experience on Buderus or Worcester Bosch Group appliances. You can find Gas Safe registered engineers at gassaferegister.co.uk.
Parts you may need
- KIM (Key Identification Module) · from £60
- UBA 3 burner control board · from £280
- Mains transformer · from £55
- BC10/BC20 controller interface module · from £120
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 £150–£450, depending on the underlying cause.
Frequently asked questions
Can I fix Buderus fault code 9P myself?
The only safe DIY step is resetting the boiler once or twice. All the physical work — reseating the KIM, replacing the KIM module, or diagnosing a UBA 3 board fault — involves opening the boiler casing and working on its electrical control components. This must be carried out by a competent engineer; in the UK, all boiler servicing and repair work that involves gas or the internal electrics of a gas appliance should be handled by a Gas Safe registered engineer.
How much does it cost to fix a Buderus 9P fault?
Most people with this fault end up paying somewhere between £150 and £450. If the fix is simply reseating the KIM correctly, you are mainly paying for the engineer's call-out and time — typically £80–£150. A replacement KIM module adds around £50–£80 in parts, bringing the total to roughly £150–£280. If the UBA 3 control board needs replacing, the board itself can cost £200–£350 in parts, putting the total repair bill in the £350–£550 range. In rare cases where both the transformer and UBA 3 have failed, costs can exceed £600, but this is uncommon.
Why does my Buderus keep showing 9P after I replace the KIM?
If a brand-new KIM still triggers the 9P fault, the UBA 3 board is almost certainly the culprit — it may have an internal fuse that has blown, or the board itself has failed and can no longer communicate with any KIM. A recurring 9P after multiple resets and a new KIM is a strong indicator that UBA 3 replacement is needed. In a smaller number of cases, an ongoing electrical supply problem (low voltage, poor earthing, or stray currents) is damaging the KIM or the board — worth asking the engineer to check the mains supply integrity at the same time.
Will a Buderus 9P fault cause any damage if I leave it?
The boiler will not operate in a 9P lockout — there is no heating or hot water until the fault is cleared. There is no immediate safety hazard from the lockout itself, but leaving the boiler off for an extended period in cold weather can risk frozen pipes elsewhere in your home. It is best to get a qualified engineer to investigate promptly rather than waiting.