Method of partially draining a central heating system

A central heating system (10, Fig. 1a) has a heating fluid viewing unit 12 on a heating fluid conduit forming part of a circuit (20, 22, Fig. 1a). The viewing unit 12 comprises a body 28 with a through bore 29 defining a heating fluid flow path and a light transmissible portion 40 for viewing the through bore 29. The viewing unit 12 is connected to the circuit (20, 22, Fig. 1a) of the system (10, Fig. 1a) by first and second conduit couplings 30, 32. The system (10, Fig. 1a) is drained by opening the circuit (20, 22, Fig. 1a) at a draining point (64, Fig. 1a), monitoring the light transmissible portion 40 of the viewing unit 12 to determine when heating fluid 46 in the circuit reaches a predetermined level, and closing the circuit to stop the draining. A method of monitoring and purging the system (10, Fig. 1a) of airlocks and a method of inspecting heating fluid 46 in the system (10, Fig. 1a) by determining its colour is also claimed.

Method of partially draining a central heating system