HAMWORTHY HEATING LTD
21
PUREWELL VariHeat he
500001155/F
8.5 Heat
Demand
Depending upon the setting of parameters, the demand can be activated under the priorities detailed in figure
8.5.1
During normal operation, if the flow temperature exceeds it’s maximum setting, all further demands are blocked
and a programmable anti-cycling timer starts. The block will be removed when the flow temperature has dropped
below the offset maximum value. In addition, there is a hysteresis band on the return temperature at the
instigation of the block, which ensures that the boiler will be blocked, should the flow temperature drop very
quickly, until the return temperature is outside of the hysteresis band - see figure 8.5.2.
Each heat demand (Cascade, BMS, Heating etc.) has it’s own set of parameters for setting the offset and
hysteresis.
Heat Demand
Activated by
Mutual Priority
Service Mode
Display Screen
1
Cascade
RS 485 Protocol
2
Boiler Management System
Analogue Input (0~10 Vdc)
3
Heating
Remote On/Off or Thermostat
4
Frost Protection
Low return temperature
5
Figure 8.5.1 - Priority Heat Demands
Figure 8.5.2 - Temperature Offset and Hysteresis
8.5.1
Service Mode
The Service Mode can be only accessed if the boiler does not display a ‘lock-out’. To clear a ’lock-out’ press the
enter button to reset the boiler. To access the service mode press the ‘Exit Button’ for 5 seconds. A four digit
numerical code must be entered to enable the engineer to access the programming functions necessary to
commission the boiler. Use the buttons with vertical arrows to select each number (from 0-9) in the 4 digit code
required. The horizontal buttons enable a position in the four digit sequence to be selected. As soon as the correct
code has been entered, the Service Mode will start (refer to Hamworthy Heating Ltd for service code). To exit the
Service Mode press the on/off (Enter) button. If during Service Mode operation, no buttons are pressed, after 40
minutes the boiler will revert back to normal operation under the previous demand. Activation of the Service Mode
overrides all other heat demands. During Service Mode, all safety devices remain active with the flow temperature
controlled to the maximum setpoint.
When entering the Service Mode, the fan speed will be held at the level prior to entering Service Mode and if in
Standby, will be held at the ignition speed. During the Service Mode function, the fan speed can be adjusted by
pressing buttons 1 or 3 to achieve the desired level (in increments of 10 rpm). After changing the fan speed, the
screen will display the new setpoint for 3 seconds and then revert to the boiler ON Status Display screen—see
figure 8.7.
