hi mark
heres a previous post of mine ..it may help
i have just been getting my van ready for a couple of days away. All the tanks and boiler were drained down . I filled the cold water tank and ran the hot and cold water , cold was ok but as i hadnt closed the drain plug on the carver i (unsuprisingly) couldnt get water from the hot tap . Once i had closed it water came through ok ( huge relief , no burst pipes). I switched the boiler on but it cut out after the 10 second starting sequence ..i re tried about 20 times to no avail. After reading the manuals etc i resorted to tinternet and found i wasnt the first person to do this. The problem is that the burner module fills with water splashing back from the drain valve, it can also happen during adverse weather apparently, So if your carver switches to the red light after 10 seconds or so that may be the problem. Easily sorted by removing the outside cover and inner plate which covers the module and drain the water off . Disclaimer ..........dont mess around with gas unless you are 100% confident in what you are doing , but this is no more difficult than changing a cylinder