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
   both
   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.