Potterton 7668920, Engineer'S Service Manual

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3. Sequence of Operation
Mains ON
(CH or DHWdemand)
Self-test cycle for 20 s
(output setting displayed)
Flow temperature
less than set point
10 second pre purge
5 second ignition
Flame detected 5
th
ignition attempt
NO
Ignition lockout
Burner ON
Modulate output
Flow temperature or
rate of rise too high
NO
Burner OFF
Over temperature
fault
Lock out
Mains OFF
(demand satisfied)
NO
1. Switched Live On: When the boiler switched live
turns on the boiler, a 20 second check cycle takes
place. If the flow temperature is less than the boiler
set-point temperature the ignition cycle will start.
Pre-purge, Ignition and Burner on.
2. Fan Pre-Purge: The boiler has a 10 second
pre-purge (Fan On, Spark Generator and Gas Valve
off) before the start of the ignition sequence.
3. Ignition: The boiler has a 5 second ignition period
(Fan, Spark Generator and Gas Valve on) and burner
on occurs when a flame is detected. If a flame is not
detected within the 5 second ignition period then 4
more ignition attempts are made. If a flame is not
detected after the 5 ignition attempts the boiler goes
to an ignition lock-out and an error light is displayed.
4. Burner on: After a successful ignition, Burner on
occurs (Fan and Gas Valve on, Spark Generator off).
The boiler flow temperature is controlled by varying
the fan speed (and thereby the gas rate) to achieve
the optimum boiler operation. If the boiler flow
temperature exceeds the boiler set-point, the burner
will turn off (Fan and Gas Valve off).
5. Over temperature: If a boiler over temperature
event occurs (triggering the safety thermostat) the
burner shuts down (Fan off and Gas Valve off). A
locking signal is generated and an error lightis
displayed.6. Lockout: If a lock-out error is displayed
(Fan, Spark Generator and Gas Valve off) the boiler
can only be reset by manually pressing the reset
button. If 5 lock-outs are reset within a 1 hour period
then a hard reset is required see section 8.1.3
Baxi Customer Support 0344 871 1525
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