Section 8: Electrical
Page 25
! WARNING !
After completing electrical connections and before
reconnecting the electrical supply to the boiler, replace
the terminal block cover and secure it using the screws
provided.
13. Re-connect the electrical supply and check operation of
heating system controls (programmer, room thermostats,
etc.).
14. Refer to Instructions provided with the programmer for
operation and setting.
15.
Leave the Programmer and Thermostat Instructions with the
user after installation for their future reference.
* Cable colours corresponding to 4-core cable conforming to BS
EN 50525-2-11.
BURNER LEAD PLUG/SOCKET CONNECTOR
On all models, the electrical cable between the boiler control
panel and burner is now fitted with an in-line 4-way plug
and socket connector. This enables the burner to be easily
disconnected from the boiler control panel for ease of removal for
servicing.
8.2.2 CIRCULATING PUMP
On the Internal System models, the circulating pump is factory
fitted within the boiler enclosure and the pump is wired to the
pump terminals on the control panel terminal block.
On Internal models the pump should also be connected directly to
the control panel terminal block. Refer to Section 8.2.1.
Connecting this way allows the pump to be isolated using the
Boiler ON/OFF switch, on the boiler control panel, for servicing or
maintenance work.
Also, the boiler control automatically provides a short pump
‘overrun’ (two minutes) after the burner is shut down (when the
heat demand is interrupted), e.g. when the room thermostat is
satisfied. This pump overrun will not occur if the boiler power
supply is interrupted, e.g. if the boiler ON/OFF switch is set to off.
8.3
CONNECTING AN EXTERNAL FROST
THERMOSTAT
The boiler is fitted with two forms of pre-set internal frost
protection, as follows:
Water temperature:
Should the central heating water temperature (detected by the
flow thermistor) fall to below 8°C this frost protection function will
be activated and will operate as follows to protect the boiler from
freezing:
•
The heating circulating pump will run for a period of 15
minutes. If during this time the water temperature exceeds
15°C the pump will stop.
•
If after the 15 minutes the temperature is less than 10°C the
burner will fire and continue to do so until the flow thermistor
detects a temperature of 30°C when the burner will stop.
The heating circulating pump will then run for a period of 2
minutes before also stopping.
Air temperature:
Should the air temperature around the boiler fall to below 5°C
this frost protection will be activated and will operate as follows to
protect the boiler from freezing:
•
First the heating circulation pump will operate for a period
of 15 minutes. If after that time the air temperature sensed
exceeds 10°C the pump will stop.
•
If after the 15 minutes the temperature is less than 10°C the
burner will fire and continue to do so until the flow thermistor
detects a temperature of 30°C when the burner will stop.
The heating circulating pump will then run for a period of 2
minutes before also stopping.
For additional protection of either the entire heating system, or
any exposed parts of the heating system (e.g. if the boiler is
installed in an external boiler house, un-heated garage or attic)
a remote frost thermostat can be connected to the boiler. This
will operate in conjunction with the internal frost protection and,
when activated, the boiler will operate as described at the start of
Section 8.3.
This remote frost thermostat should be sited within the house in
such a place that any rise or fall in ambient air temperature can be
detected, i.e. in a room with a radiator.
To connect a remote frost thermostat (for example, a Danfoss
Randall RET230F), proceed as follows:
1.
Lift off the boiler case top panel, if it has not already been
removed.
2. Loosen (do not remove) the four screws securing the control
panel to the side panels, hinge the panel forward and allow it
to drop down to gain access to the top of the panel.
3. Remove the two screws securing the terminal block cover
and lift off the cover.
4. Remove the screws securing the cable clamp and open
clamp.
5.
Connect the wires from the frost thermostat to terminals on
the control panel as follows:
•
Frost thermostat Neutral (N) to terminal 21 on PCB
connector.
•
Frost thermostat Live (L) to terminal 24 on PCB
connector.
•
Frost thermostat Switched Live-ON (3) to terminal 23 on
PCB connector.
6. Refer to Figures 8-1 and 8-2 for typical connection of Remote
Frost Thermostat.
7. If an alternative Frost thermostat to the Danfoss Randall
RET230F is used, connect it in accordance with the frost
thermostat manufacturer’s instructions.
8.
Make the remaining required connections to the control
panel, as detailed in this section.
9. Secure the cable clamp.
10.
Re-fit terminal block cover on control box and fasten with the
two screws previously removed.
11.
Close the hinged panel and tighten the four screws securing
the control panel to the side panels.
12. Replace top casing panels.
! NOTE !
This external frost thermostat will operate in parallel with
the internal frost thermostat.
! NOTE !
For total system protection against freezing, particularly
during extended periods without electrical power, Grant
recommend the use of a combined heating system
antifreeze and corrosion inhibitor, used in accordance with
the manufacturer’s instructions.