Aztec boilers are approved for use on fully pumped open vented
systems and sealed systems. When fitting on a sealed system a 3 bar
safety valve must be fitted to the system, where thermostatic
radiator valves are fitted it will be necessary to fit a bypass to obtain
minimum flow rates.
IMPORTANT: IF MIN FLOW RATES ARE NOT OBTAINED THE BOILER
MAY GO TO LOCK OUT ON HIGH LIMIT THERMOSTAT.
Where more than 1 boiler is fitted refer to multiple boiler
installations.
System must be flushed out before adding inhibitor to BS 7593:1992
Treatment of Water in Central Heating Boiler.
IMPORTANT: THIS BOILER IS TO BE FITTED ON FULLY PUMPED
SYSTEMS ONLY.
Sealed Water System Requirements
The installation must comply with the appropriate requirements of
the current issue of BS 4814, BS 5449, BS 6798 and BS 7074 Part 1
and 2.
THE INSTALLATION ENGINEER MUST BE REGISTERED AS A
COMPETENT UDHWSS INSTALLER.
Safety Valve
A safety valve set at 3 bar must be fitted with the drain routed to
the outside of the building. The drain must not discharge above an
entrance or a window or any public access area, be clear of any
electrical fittings and positioned so that any discharge can be seen.
Expansions Vessel Capacity
A diaphragm type expansion vessel, conforming to the current issue
of BS 4814. The expansion vessel must be connected to the systems
at a point close to the inlet side of the circulating pump. The
expansion vessel volume depends on the total water system volume
and the initial system design pressure. For any system an accurate
calculation of vessel size is given in the current issue of BS 5449 and
BS 7074 Part 1.
The water content of the boiler is given in the Technical
Specification. Note: A higher initial design pressure requires a larger
volume expansion vessel.
The charge pressure must not be less than the static head of the
system that is the highest point of the system above the expansion
vessel.
Capacity of Expansion Vessel
Where design information is not complete the following chart (Page
9) can be used for selecting the size of the vessel, it should be noted
that the size given in the table account of fault conditions.
System Temperature
The normal running temperature of the system is 75°C, if a fault was
to occur then the safety device would allow the system temperature
to rise to 100°C. It is recommended that this figure be used in the
calculations of vessel size.
Connection of the Expansion Vessel
The expansion vessel should be connected in the neutral part of the
system this being the return pipe work close to the boiler, refer to
sealed system pipe work layout drawing (Fig 11).
Pressure Gauge
A pressure gauge must be permanently fitted in the system covering
a range from 0 to 4 bar. Position where it can be seen when filling
the system.
Inhibitor
If using an existing system, take care to drain down the entire
system including the radiators then thoroughly clean out before
fitting the boiler. Attention is drawn to the current issue of BS 5449
and BS 7593 on the use of inhibitors in central heating systems.
Drain Tapping
A drain tapping must be provided at the lowest point of the system,
which will allow the entire system to be drained.
Note: Failure to ensure the correct vessel size could result in
premature failure of the expansion vessel which in turn may
adversely affect other components in the system i.e. circulating
pump and diverter valve.
System Make-Up
Water loss from the system should be replaced from a make-up
vessel connected to the system. This vessel should be higher than
the top of the system. Alternatively provision can be made by pre-
pressurisation of the system via a temporary hose connection and
through a double check valve (non-return) and stop valve. There
must be no permanent connection to the mains water supply even
through a non-return valve.
Alternative Methods of Filling Sealed System
