Worcester Bosch 24CDi not working

Worcester Bosch 24CDi combination boiler not working for heating or hot water. Boiler starts to run on demand, pump and fan starts. Ignition spark can be heard but not lighting at the burner.

I remove the combustion casing so I can see the ignition electrodes, and demand heating from the boiler. Again it runs, and tries to light. There is a good spark at the electrodes, but still not lighting the burner. I replace the cover and undo the gas inlet test nipple to ensure there is gas supply to the boiler. There is a smell of gas and my manometer is registering approximately 20 mbar pressure. Firing the boiler has no effect on the gas supply pressure, so it is looking like the gas valve is not opening. The boiler manual tells me to check the resistance on the two purple and two brown wires to the gas valve, it should be less than 100 ohms. one of the wires is showing 24 kohms. I check the cable for continuity, which is fine on all four wires. The manual suggests the problem definitely is the gas valve.

After replacing the gas valve, I create hot water demand, setting the burner pressure to maximum on the rear of the PCB housing. Using a 2mm allen key I adjust the burner pressure to 13.2 mbar. I check the minimum burner pressure setting, again by adjusting the setting on the rear of the PCB housing. The burner pressure is 1.8 mbar and does not require adjusting using a 3mm allen key. I reset the burner pressure to normal on the rear of the PCB housing and put all the casing back on the boiler.

Disclaimer: The works described in this blog are a record of work undertaken and should not be taken as guaranteed to solve your problem. Work should only be carried out by persons qualified and competent to do so.