3.0 Appliance Operation
8
© Baxi Heating UK Limited 2005
NOTE: All delay timers mentioned in 3.1 and 3.2 are
overridden by domestic hot water demand.
3.1
Central Heating Mode
1. With a demand for heating, the pump circulates water
through the primary circuit. At a flow rate of
approximately 4.5 l/min the central heating flow switch
operates, initiating the ignition sequence.
2. The main burner ignites at a low rate, then the fan/gas
valve and proportionator control the gas rate to maintain
the heating temperature measured by the thermistor
sensor.
3. When the flow temperature exceeds the set
temperature, a 1 minute pump overrun occurs followed
by 3 minutes anticycle. If the flow temperature is low
enough the burner will then relight automatically
otherwise pump overrun and anticycle will occur again.
4. When the demand is satisfied the burner is
extinguished and the pump continues to run for a period
of 1 minute (Pump Overrun).
3.2
Domestic Hot Water Mode
1. Priority is given to the domestic hot water supply. A
demand at a tap or shower will override any central
heating requirement.
2. The flow of water will operate the DHW flow switch
and the 3-way valve will change position. This will allow
the pump to circulate the primary water through the
DHW plate heat exchanger.
3. The burner will light automatically and the temperature
of the domestic hot water is controlled by the return
thermistor.
4. When the domestic hot water demand ceases the
burner will extinguish and the diverter valve will remain in
the domestic hot water mode, unless there is a demand
for central heating.
3.3
Boiler Frost Protection
1. The boiler incorporates an integral frost protection
feature. It will operate in both summer and winter modes.
If the boiler temperature falls below 8°C (± 5°) then the
boiler will fire until a temperature of 15°C (± 5°) is
reached.
3.4
Pump Protection
1. The control system continually monitors the time since
the pump last operated. This will result in the pump being
run for 1 minute if it has not run in the last 24 hours to
prevent seizure.