Error F1 259

Safety precautions:

- Do not attempt to work on gas or mains wiring unless you are a qualified Gas Safe / electrical engineer. Improper work is dangerous and illegal.

- Before opening the boiler case, switch the boiler off at the isolator and turn off the mains electrical supply to the boiler. Wait a minute to ensure capacitors discharge.

- If you suspect water ingress or visible leaks, isolate the water and power and do not run the boiler.

Initial checks a homeowner can do:

1) Record the full displayed fault: note the F1 259 and any accompanying flashing lights or additional cause codes shown in the info menu (press the spanner or information button on the control panel to view cause codes). Take a clear photo for the engineer.

2) Try a controlled reset: with the boiler powered, press and hold the reset (or ✔) button for about 8 seconds until the display reboots. If the boiler clears and runs normally, monitor for recurrence. Do not repeatedly reset a locking fault more than once or twice.

3) Power-cycle the boiler: switch off at the isolator or consumer unit, wait 60 seconds, then switch back on. This can clear transient electronic faults caused by power spikes.

4) Check for recent work or disturbances: has anyone worked on pipework, electrics, antenna/code plug, or replaced a module recently? Note any recent water leaks, condensation, or blocked flue which may have affected electronics.

5) Check external controls and wiring: ensure room thermostats, timers, or smart controls are powered and calling correctly. A communication fault from an external control can sometimes look like a control error.

Basic safe visual inspection (only after power isolated):

1) Remove the outer case only if you are comfortable and the power is isolated. Do not touch live components.

2) Visually inspect the PCB area and HCM for loose plug connections, bent pins, or obvious burn marks, corrosion or water staining. Pay attention to the HCM seating and the coding card/plug if fitted.

3) If a connector appears loose, you may carefully reseat it (push gently but firmly) only after power is off. Do not attempt to solder or rework the PCB yourself.

What to tell the engineer and when to call one:

- If reset and power-cycle do not clear the error, or the fault reappears, stop further attempts and call a Gas Safe qualified engineer or Worcester Bosch service if under warranty.

- Report the exact fault code F1 259, any additional cause code from the info menu, what you observed (photos if available), any visible damage, and the steps you have already tried (reset, power-cycle, reseated connectors).

- Advise the engineer if the boiler is still under warranty and who installed/serviced it previously.

Why a professional is required and typical next steps by an engineer:

- A Gas Safe engineer will run diagnostic tests (access service/info menu, check communication between HCM and PCB, check coding card, run component tests for fan/ionisation/pump), measure voltages and continuity, and confirm whether the HCM or the main control box/PCB is defective.

- Repair actions may include cleaning/replacing a corroded connector, fitting the correct HCM or code plug, replacing the HCM or control box, or addressing an underlying cause such as water ingress. These are specialist tasks involving sealed gas components and live electronics and must be done by a qualified engineer.

Do not continue to operate or repeatedly reset a boiler showing F1 259. If you are unsure at any stage, isolate power and call a Gas Safe registered heating engineer or Worcester Bosch support with the fault details.