When there is a demand for heating (either from the room
thermostat or the clock) and the boiler temperature control is
calling for heat. The pump starts and at a flow rate of 4 Itr/min
the central heating flow switch operates allowing the ignition
sequence to begin. The first stage solenoid 12a Fig. 7 and
safety solenoid 12c Fig. 7 open together to allow gas to the
burner. The ignition sequence begins and a continuous high
speed spark ignites the gas. As soon as a flame is detected the
orange indicator bulb b 23 Fig. 6 will light. After 45 seconds the
second stage solenoid 12b Fig. 7 opens to allow the full gas
rate. If a flame is not detected, after 8 seconds, the security
solenoid closes and shuts off the gas. The red lockout indicator
bulb * 24 Fig. 6 will light.
The central heating flow temperature is controlled by the
central heating control thermistor 16 Fig. 7. The boiler has been
designed to minimise cycling and will not attempt to relight for at
least 3 minutes after the boiler thermostat has been satisfied.
When the room thermostat is satisfied the burner will switch off
and the pump will remain running for a further 3 minutes before
it to stops.
NB
It is possible to override the 3 minute delay by pressing the
RESET button 25 Fig. 6.
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