5
Super Plus -
Installation and Servicing
GENERAL
LEGEND
1.
Flue test point
2.
Water header
3.
Gas pressure test
point
4.
Module
5.
Module upper cover
6.
Module lower cover
7.
Gas header
Fig.1 Boiler Assembly - Exploded View
GENERAL
Regular maintenance by competent personnel is essential
to the safe and reliable operation of the boiler. Full details of
these requirements are given in these Installation & Servicing
Instructions.
BOILER DESCRIPTION
Each boiler consists of the following packs:
(a)
The insulated stainless steel casing with flue outlet, condensate
drain, wiring centres and wiring harnesses and for 300/3 or
500/5 boilers only, blanking kit.
(b)
Boiler modules.
(c)
Gas header, flow and return water headers and module
fixing packs.
(d)
Extra blanking kit and support bracket kits for the 300/3
Alternative and 400/4 Alternative boilers only.
Note:
The 300/3 Alternative and 400/4 Alternative are sold with
a view to later upgrading.
MODULE DESCRIPTION
The module can be subdivided into 3 main elements:
(a)
The heat exchanger consisting of finned aluminium tubes
expanded into cast aluminium tube plates. The bottom cover
plate is cast aluminium. The top cover plate is cast iron, fitted
with cast iron flow and return elbows.
(b)
The gas line which supplies and regulates the gas flow to the
main burners.
(c)
The controls assembly which incorporates the fan (supplying
air for combustion) and the electrical controls.
The normal mode of operation of the boiler (described below) is
preceded in certain conditions by a phase in which the complete
boiler casing is given a 5-volume air change. This air change is
an important safety feature of BS.5978 and will occur whenever
the boiler goes from a situation of no modules firing to a situation
of one module firing. This includes morning start-up and those
occasions of low load when the last module firing goes off on its
thermostat (or external controls) and is then called again. The air
change will NOT occur if one or more modules are firing and a
further module is called.
The 5-volume air change phase operates as follows:
All the module fans are energised and run for approximately 70
seconds. At the end of this period all the fans are switched off
except for that on the module being called which then immediately
enters its 35 second, pre-purge period, (see Fig. 20).
When the electronic control thermostat calls for heat, the fan is
switched on and purges the combustion chamber for approximately
35 seconds. At the end of this period the ignition sequence starts:
The spark generator is energised and delivers a spark to the main
burner and at the same time the main gas valves are opened.
Once the flame is sensed and proved by the flame detection
probe, the controls keep the main gas valves open until the control
thermostat is satisfied.
The module is protected against blockage of burner, heat
exchanger, flue or fan by the pressure switch. This senses the
differential pressure between the pressure in the fan housing
and the suction in the venturi casting, preventing the ignition
sequence starting or causing safety shut down should the pressure
be outside the design limits. After combustion, the products flow
past the finned aluminium tubes, and through the gas distribution
screen into the boiler casing, transferring heat to the water flowing
through the tubes.
Each module is connected in parallel across the flow and return
water headers, so that water is flowing through all the modules
at all times.
