Glow-worm 56/3e Back Boiler - Manual (Page 17)

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6 Commissioning
6.1 Commissioning the Back Boiler
Before commissioning the back boiler, the whole of the system
should be thoroughly flushed out with cold water with the
circulation pump removed. Replace the pump, fill the system
and examine for water soundness. Vent air from the system and
pump.
The back boiler unit is fitted with a flue blockage safety device,
which will shut it down if there is a lack of oxygen. The principle
by which this operates is that when there is a depletion of
oxygen resulting from a build up of combustion products, flame
on the pilot light will become unstable and lift up off the
thermocouple. This will deactivate the mag unit in the gas
control valve, cutting off the gas supply.
If the back boiler unit shuts down frequently for no apparent
reason the first things to be checked are the chimney and air
inlets into the room. Any problems found must be put right, by
a competent person, and a full operational test carried out
before the back boiler unit is used again.
The flue blockage safety device incorporates the electrode,
thermocouple and pilot assemblies.
The flue blockage safety device MUST NOT be adjusted or
disconnected. It must be serviced strictly in accordance with the
instructions in this book. Any unauthorised interference could
result in the device failing to operate, creating a potentially
dangerous situation. If replacing, use only the correct and approved
part.
CAUTION: The following work should be carried out by a
competent person.
Identify the back boiler controls by reference to diagram 6.1.
Note: Overheat cut-off, see diagram 6.1 is applicable only
where the back boiler unit is incorporated in a sealed water
system.
Open all windows and put out any naked lights, cigarettes etc.
Test the gas supply for soundness. Purge air in accordance with
the current issue of BS6891.
Check that the electrical supply to the back boiler is switched off.
Set the control thermostat knob “A” to “0”, “Off” position that is,
fully anti-clockwise, see diagram 6.1.
Make sure the thermostat phial is fitted correctly, see diagram
5.4.
Remove the back boiler burner pressure test screw “B” and
connect a suitable pressure gauge.
Turn gas service cock “D” to the “On” position making sure that
the fire front service cock “D” is in the “Off” position, see diagram
4.12.
Technical Sequence of Operation
When an external control calls for heat there is approximately
a 30 second purge. The control board (PCB) energises the
thermoelectric valve and spark unit. With the thermoelectric
valve open gas is allowed to pass to the combustion products
discharge safety device which will be ignited by the sparks.
This ignition attempt will continue until the milli-voltage generated
by the thermocouple is sufficient to hold open the pilot valve. At
this point the thermoelectric valve and spark unit are de-
energised and the green light on the lockout reset button “E” will
illuminate, see diagram 6.1. The main gas control valve is
energised through the closed contacts of the control thermostats.
When the water temperature has reached the set point the
control thermostat contacts open, the main gas control valve is
closed. The pilot will, however, remain alight since the
thermocouple is generating the required milli-voltage.
When the water temperature falls below the set point the control
thermostat control will close, thus energising the main gas
control valve and allow the main burner to light from the pilot
light.
The boiler will continue to cycle in this manner until the external
control stops its demand for heat. At this point external power
is removed the main gas control valve and the thermocouple
milli-voltage is reduced to zero.
That is to say whilst ever there is a demand for heat from an
external control the pilot will remain alight despite the boiler
thermostat cycling on or off.
Check the pilot flame is stable and has a length as shown in
diagram 6.2.
Note: Should the red light on the lockout reset button “E” come
on, it indicates that the pilot light is not operating correctly, or the
combustion products discharge safety device has been
activated.
Depress the lockout reset button “E”, when the fault has been
corrected indicated by the green light illuminating, see diagram
6.1.
Turn control thermostat knob “A” clockwise until “MAX” is
against the pointer positioned on the control box front cover “F”.
The main burner will light.
Test for gas soundness using a suitable leak detection fluid.
Diagram 6.1
6821
CONTROL BOX
LOCKOUT
RESET
BUTTON “E” CONTROL
THERMOSTAT
KNOB “A” OVERHEAT CUT-
OFF DEVICE
(sealed systems only)
PRESSURE TEST POINT “B”
ELECTRICAL
PLUG
GAS CONTROL VALVE
GAS SERVICE
COCK “D”
POINTER
“F”
ADJUSTER “G”
GREEN
RED