Assessment Paper

Students Name:

Section 1

  1. A variable potentiometer gives a change in voltage at its output.

  2. The variable potentiometer controls:-
    central heating flow temperature
    domestic hot water temperature
    flue gas temperature

  3. If the overheat device operates it:-
    isolates power on the appliance
    isolates power to the pump
    isolates power to the clock
    allows appliance to fail safe

  4. Show different wiring diagrams. These may include connections to the 3-amp spur, the clock, the room stat and other parts.

  5. The hydraulic valve is operated by:-
    wax capsule
    electric motor
    heat exchanger
    differential water pressure

  6. The NTC controls:-
    voltage to diagphragm pump
    voltage to solenoid operator
    voltage to pump
    ignition transformer

Section 2

The following information is needed to do practical exercises on the chosen systems:-

  1. Visual check of appliance.

  2. Pump and water deficiency valve.

  3. Voltage readings for microswitches.
    microswitch off hot water heating
    M1 V dc V dc V dc
    M2 V dc V dc V dc

  4. Voltage readings for servo valve and microswitch M3.
    open circuit: V dc closed circuit: V dc

  5. Check fan pressure switch.

  6. Identify the position of the following and put the voltages into the table.
    1. diaphragm pump
      maximum V dc
      minimum V dc

    2. main transformer
      primary circuit V ac
      secondary circuit V ac

    3. overheat/limit thermostats and check wether open or closed circuit.

    4. electronic boards - visually check sequence of relays using sequence of events information.