f25 fault on glow worm boiler

One day, the F25 error code appeared, and we did the whole load of troubleshooting and tried all possible actions. When none of them worked, we called a British Gas engineer, who fixed it by installing a couple of automatic bleed valves at our airing cupboards’ bleed points. The problem had been caused by air getting trapped in and around the pump and valves, which we could not bleed manually.