Glowworm Heat Exchangers (Page 10)
There are two types of heat exchanger that can be present, the primary heat exchanger and the secondary heat exchanger. The primary is present in almost all boilers and it allows the heat to be transferred from the burner to the water within the system. The secondary heat exchanger only appears on combination boilers and allows the heat to be transferred between one closed system and another.

GLOWWORM 2000801885 O RING HEAT EXCHANGER PIPE (PK50) - NOW USE 1416322
Part No: 1331419 / MPN: 2000801885