Waj Tohir
The pipe work under your boiler consists of a gas pipe, mains pressure water, hot water to taps, flow to radiators and return from central heating. Also, White plastic pipe is for condensate and a pipe which deals with getting rid of water in the event that the boiler gets over pressurised. To pressurise your boiler, mains pressure water has to be fed into the central heating return pipe. This is done via a filling loop. One end of the loop is attached to the mains pressure and the other end is attached to the central heating return pipe. This can be a factory fitted loop (which doesn’t look like a loop) found directly under the boiler. Or it can be a silver coloured flexible loop fitted usually a little bit below the boiler but could in theory be anywhere eg if the boiler is in a loft, the filling loop and a pressure gauge might be in the old airing cupboard to save the user climbing up into the loft to fill the system. The correct name for a filing loop is “temporary filling loop.” The user is supposed to open the valves, fill the system, close the valves and then remove the filling loop. This is done for safety reasons: if the valves fail, or start to pass water, the boiler could get over pressurised as a result. Where is your filling loop? I don’t know - would need photos etc to point it out.
