Overview
F0 279 on a Worcester Bosch GB162 indicates a fault with the burner control unit (sometimes called the KIM or electronic control module). The cause code 279 is associated with an A/D converter reference or sensor test error inside the control electronics, meaning the board is not correctly reading signals from sensors or converting analogue inputs. When this fault appears the boiler may lock out or refuse to fire because the control cannot verify safe operating conditions. This is a serious electrical/electronic fault rather than a simple user-level issue. Common triggers are failed electronic components, corrosion or water ingress into the control box, damaged connectors, voltage spikes, or an incorrect/failed coding card or HCM. A homeowner can perform a few basic checks (reset and power-cycle, look for obvious water or damage), but replacing or repairing the burner control unit requires a qualified Gas Safe or equivalent engineer due to live electrical circuits, fuel supply, and safety-critical testing. Do not attempt to run the boiler repeatedly if the fault persists — it should be isolated and inspected by a professional.
Possible Cause: Control unit may need replacing.
Troubleshooting Steps
Safety precautions:
- If you smell gas, leave the property immediately and call your gas emergency number. Do not operate electrical switches or the boiler.
- Isolate the boiler by switching off the electrical supply at the fused spur or consumer unit before touching any external covers. If you are not competent with electrical work or gas appliances, do not open the boiler.
- Do not attempt to replace the control unit or internal components unless you are a Gas Safe registered engineer (or equivalent for your fuel type).
Initial checks a homeowner can do (non-invasive):
1. Record the exact fault code and any cause code shown in the information menu. Note when it happened and any conditions (power cut, storm, recent service work).
2. Try a standard reset: press the reset button per the boiler manual (usually hold for 3 seconds) or switch the boiler off at the fused spur for at least 30 seconds and then back on. Observe if the fault returns immediately or after a few cycles.
3. Power-cycle the boiler: turn off mains power to the boiler for 5–10 minutes, then restore power and check for the code reappearing.
4. Look for obvious signs of trouble around the boiler: water leaks, corrosion, burn marks, loose external wiring, or a frozen condensate pipe. Do not open the control box.
5. Check that the house electrical supply and the boiler’s fused spur/fuse are intact (a blown spur fuse may show as power issues). If unsure, contact a qualified electrician.
Specific diagnostic guidance and next steps (for information and to prepare when you call an engineer):
1. If the fault clears and does not return, monitor the boiler for a short period. If it reappears, stop using the boiler and book an engineer.
2. If the fault persists after reset/power-cycle, do not keep resetting repeatedly. Multiple resets can mask an underlying failure and are not a safe long-term fix.
3. Prepare information for the engineer: exact fault code (F0 279), any cause code shown in the info menu, how long the fault has been present, any recent maintenance or power events, and whether you observed water or smell of burning.
4. If you can safely view the external wiring and connectors without opening the boiler, check for visibly loose plugs or disconnected leads at accessible terminals. Do not remove internal covers.
5. If you suspect water ingress (wet components, visible rust, or pooling) or if the boiler has suffered a power surge, mention this — both can damage the control unit.
What a qualified engineer will do (so you know what to expect):
- Carry out safe isolation and open the boiler to inspect the burner control unit (KIM), connectors, and nearby wiring for corrosion, moisture, or thermal damage.
- Use diagnostic tools to read full fault history and live sensor values, test the A/D converter and related sensor circuits, and confirm whether sensors, wiring, or the control board itself is at fault.
- Replace the burner control unit or code plug/HCM if necessary and verify correct programming/coding card for your GB162 variant.
- Run safety and ignition checks, check flame sensing and gas/oil supply circuits, and confirm the boiler operates normally before leaving.
Final note: F0 279 is not a DIY repair. Contact a Gas Safe registered engineer (or relevant qualified service for your fuel) and provide them the fault code, cause code and the steps you have already performed. Leaving an electronic control fault unaddressed can prevent safe operation of the appliance.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Worcester Bosch GB162 Boiler.