4
23
4.7 - DOMESTIC HEATING & HOT WATER - REGULATIONS & GUIDELINES
When the system is cold and filled to initial fill pressure
P
i
, the pointer on the pressure gauge should point at
1 bar.
The pressure gauge shown has two red zones marked
on it. The first is between 0 and
1
/2 a bar. If the pointer
falls into this zone when the system and the boiler are
cold, this indicates that the initial system fill pressure
has dropped. This will activate the pressure switch,
cutting off power supply to the Combi or System
boiler. Refill the system manually until indicated
pressure rises to 1 bar.
N.B. Insufficient pressure in the boiler will cause
power supply to switch off.
* A 12 litre expansion vessel is fitted to the boiler,
precharged with air or nitrogen to 1 bar, which allows
a system static head of 5 metres. If the static head is
greater than this, the air charge in the vessel must be
increased to balance the higher static head. The air
charge should not exceed a pressure of 1.5 bar.
The Firebird Combi boilers with built in expansion
vessels have an initial air charge pressure of 1 bar. If
the total water content of the system is greater
than the capabilities of the vessel supplied, then an
additional vessel will be required to be fitted to the
return pipe, as close as is practical to the boiler.
There should be no valves or restrictions between
the vessel and the boiler. See page 24 for vessel
sizes.
If the static head is altered, it is also necessary to alter
the air charge pressure to equal static head (+ 0.3 bar).
This is necessary in order to keep the system water
from entering the expansion vessel until the system is
being heated and thus allow its maximum acceptance
volume (V) to be used only to accommodate the
expansion of system water during boiler operation.
Remember that the air charge pressure must be equal
in both vessels (attached to the same system). In the
above example this is 1 bar.The air charge pressure is
the air pressure in the expansion vessel before the
system is filled. It is measured with a tyre gauge
attached to the Schrader valve on the vessel.
SEALED HEATING CIRCUIT
(also applies to System Boilers)
The system must comply with BS 7074 Part 1 and BS
5449 Part 1 with a maximum water temperature of
80˚C.
* A manual reset overheat limit thermostat is located
at the rear of the electrical control panel (see page
51 & 52). If a boiler overheat condition arises, the
burner will stop and remain inoperative until this
thermostat reset button is depressed.
* A pressure relief valve to BSEN 4126 Part 1: 2013,
operating at 3 bar (45 lb/in
2
), is fitted. A discharge
pipe of 15 mm diameter is also fitted to the
discharge connection on the pressure relief valve.
During installation, an extension pipe should be
fitted to this, leading to outside the building. The
pipe should be as short as possible and may need a
tundish fitted in a protected position within the
building.
Note: Water must not discharge above an
entrance, window or where the public has access.
The installer must be aware that the discharge
may be boiling water.
* A drain cock must be fitted at the lowest points in
the system to enable draining as necessary. A drain
cock is already fitted at the bottom of the boiler heat
store to enable draining of the boiler and tank unit
only. All pipes connected to the boiler should have
shut off valves fitted to facilitate this.
* A pressure gauge, with a range of 0-4 bar, is fitted to
the boiler control panel. This indicates water
pressure in the boiler and the system at the time of
reading. Pressure when cold should be 0.5 bar
minimum to 1.5 bar maximum. This is known as
“Initial System Design Pressure”(P
i
).
N.B. Initial System Design Pressure (measured in
bar) equals static head of system (measured in bar)
plus 0.3.
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