Chemical testing device with a sample chamber having a piston therein with a chamber sealing element thereon

A testing device for testing a level of a selected chemical in a central heating system water in a central heating system circuit, the testing device comprising:

• a sample chamber for holding a sample of central heating system water to be tested, the sample chamber being connected to the central heating system circuit to allow fluid to pass between the central heating system circuit and the sample chamber;
• a piston for controlling filling of the sample chamber with the central heating system water from the central heating system circuit, and emptying of the sample chamber, the piston being movable to a retracted position for drawing water out of the central heating system circuit into the sample chamber, and to an extended position for emptying the sample chamber and returning the water to the central heating system circuit;
• at least one valve for isolating the sample of central heating system water from the central heating system circuit during testing;
• and
• an optical testing apparatus including a light source and a detector, for measuring an optical property of the sample of central heating system water isolated within the sample chamber and thereby making a determination as to whether or not the level of the selected chemical in the water is greater than a predetermined threshold level,
• wherein the valve for isolating the sample during testing is integrated into the piston, and
• wherein a sealing element on the piston seals the entrance to the sample chamber where the piston is in a retracted position, for preventing any further flow between the sample chamber and the central heating system circuit.