So I fitted some extra radiators to an existing heating system in a rental last autumn. The system has a permanent pilot boiler and is open-vented. Weirdly, there is no ballcock on the F&E, just a tap. I had previously advised the customer it would be a good idea to fit a ballcock, but would only be willing to do it if I fitted an overflow at the same time. Last week, the customer contacts me. Apparently the pilot light won't stay alight and so water heating often not working. I said it sounded like a boiler issue more than a controls problem and to get a gas installer. Registered gas installer reported that the boiler was cutting out due to overheating and had masses of air in it, some of which he managed to bleed out and why not get me back in as I probably had more time than he had, charged a (very reasonable) callout, and left. So I turned up today, had a fiddle with the pump, realised that the overheat mechanism on the boiler extinguishes the pilot light and realised there was no circulation in the primaries. I asked the tenant if the RGI had been in the loft. Since he hadn't, my heart leaped with joy as I guessed I had found the problem. Sure enough, I found the F&E completely empty. Filled the system and tested. All okay. Seems that checking for a seized ballcock wasn't on his check list! Customer has now finally agreed to pay for the conversion to a conventional automatic filling system.