27
e
SECTION 7
CHECKS, ADJUSTMENTS AND FAULT FINDING
7.1
CHECKING APPLIANCE OPERATION
When carrying out any repairs or servicing to the
appliance, the relevant commissioning procedure
must be undertaken to ensure the continued safe
operation of the appliance. Particular attention
should be made to ensure gas soundness, water
soundness and the electrical integrity of the
appliance.
7.2
APPLIANCE MODE OF OPERATION
NOTE: there must be sufficient system water
pressure (min. 0.5 bar) to ensure the water
pressure switch is activated. If there is insufficient
system pressure the pump and fan will be
prevented from operating.
7.2.1
SELECTOR SWITCH IN THE OFF POSITION
When the selector switch is in the OFF position,
there is no LED display or LED status indicator.
The divertor valve is in the DHW position. The
appliance will not respond to any DHW or heating
requests.
Active Functions:
●
frost-protection system
●
pump anti-block
●
valve actuator anti-block.
7.2.2
SELECTOR SWITCH IN THE HOT WATER
ONLY POSITION
When the selector switch is in the HW only
position, the status LED is illuminated and the
LED display shows the current temperature
measured at the secondary (DHW) thermistor.
The divertor valve is in the DHW position. The
appliance will respond to any DHW requests.
Active Functions:
●
DHW pre-heat
●
frost-protection system
●
pump anti-block
●
valve actuator anti-block.
7.2.3
SELECTOR SWITCH IN THE HEATING & HOT
WATER POSITION
When the selector switch is in the Heating & HW
position, the status LED is illuminated and the
LED display shows the current temperature
measured at the secondary (DHW) thermistor.
The divertor valve is in the DHW position. The
appliance will respond to any Heating or DHW
requests.
Active Functions:
●
DHW pre-heat
●
frost-protection system
●
pump anti-block
●
fan anti-block
●
valve actuator anti-block.
7.2.4 APPLIANCE FUNCTIONS
●
DHW pre-heat: this function is only active
when there are no requests for heating or hot
water. When the secondary thermistor drops
to 35
°
C, the pre-heat function is enabled, the
appliance operates on minimum power until
the secondary thermistor reaches 55
°
C.
Thereafter the pump and fan will over-run for
10-seconds.
●
Frost-protection: this function is only active
when there are no requests for heating or HW.
Should the temperature of the primary
thermistor drop below 7
°
C, the valve actuator
will motor to the heating position, and the pump
will be activated for approximately 20-minutes.
Should the temperature of the primary
thermistor excee 10
°
C during this period, the
cycle will be aborted. If the temperature drops
below 4
°
C, the boiler will operate on minimum
power until the temperature of the primary
thermistor reaches 30
°
C. Thereafter the pump
& fan will over-run for 30-seconds.
●
Anti-block cycle: when there has been no
heating or HW request for 19-hours, the anti-
block cycle is activated. The valve actuator will
motor from the DHW position to the heating
position for a period of 10-seconds and then
motor back to the DHW position. Thereafter
the pump will be activated for a period of 1-
minute. If the selector switch is in the Heating
& HW position, the fan will also be active for 1-
minute.
7.2.5
HEATING MODE
With the selector switch in the Heating & HW
position and any additional controls (time clock,
room thermostat, etc.) calling for heat, the
appliance will operate in the heating mode. The
valve actuator will motor to the heating position
and the pump and fan will be active. The operation
of the fan causes the analogue pressure switch
(PAD) to deliver a signal voltage to the control
PCB. If the signal voltage is sufficient a slow
ignition sequence is enabled, whereby the current
supplied to the gas valve modulating coil is
progressively increased from minimum to
maximum over a period of 8-seconds. During this
period the ignition electrode sparks continuously
even if the burner has ignited.
NOTE
If the spark/sensing electrode does not sense
ignition the appliance will then go to lockout.
Ignition is sensed by the electronic circuitry to
ensure flame stability at the burner. Once
successful ignition has been achieved, the
electronic circuitry allows 75% of the full gas rate
through the appliance. After 15 minutes the gas
rate is increased to maximum (100%).
When the set-point has been reached (the
position of the heating temperature selector) as
measured at the primary thermistor, the appliance
will begin the modulation phase whereby the fan
and gas valve will continuously modulate to
maintain the set-point. If the temperature
continues to rise and exceeds the set-point by
6
°
C, the burner will shut down and the boiler will
perform a three-minute anti-cycle (timer delay).
A new ignition sequence will be enabled when
the 3-minute anti-cycle has been performed and