Labour and a gasket. Guy who serviced it said it’s a forty five minute job to strip, clean and do a diagnostic check. The heater is four years old and probably only run for ten to twenty hours in total (it’s in my boat). The hire boats (narrowboats) get theirs serviced up to three times a year but they are running on red diesel.
I think a service kit which includes gaskets and glow pin is around £200 😳