Southfields Vaillant Boiler Service and F62 fault fix I had this down as a routine boiler service, but a day before, it developed a F62 fault. This is usually down to the PCB, but could also be the Gas Valve. I checked the Gas Valve and found that it was passing Gas into the burner chamber whilst off. This could create an explosive ignition which could really damage the boiler if the fan failed to operate. So whether this is the cause of the fault or not, its faulty and needs replacing. Once the replacement came I took out the old one, checked the filter and found debris from the Gas Supply had been trapped there! Good Job! Otherwise this could have been the 3rd or 4th Valve. Once the new Gas Valve was installed and tested, we still had the F62 fault, but now there was no passing Gas. A new PCB was ordered and fitted and the fault cleared! The Service then could get underway and I always like Vaillant boilers as the parts are accessible to clean. As you see by the photos before and after cleaning. I also checked the flue on this service as screws were missing from the clips, so I re-clipped it and checked that they internal flue pipe was attached all the way through. At the end when all parts are back together a Gas Analyses check is done to make sure it is burning Gas within the correct parameters set by the manufacturer. All good for another year.