A circulation pump MUST be connected to the boiler.
The boiler may be used for indirect hot water supply: wherever it is used for this type of system, an
additional heat exchanger must be provided to ensure hydraulic separation between primary and
secondary circuits.
Each boiler installation should incorporate a safety valve to ensure maximum pressure is not
exceeded.
The appliances are NOT suitable for gravity central heating nor gravity domestic hot water as system
pressure must be a minimum of 1 bar.
The boiler MUST be vented, there is an internal automatic air vent included for this purpose.
Draining taps MUST be located in accessible positions, which allow the draining of the whole
system - including the boiler and hot water storage vessel. They should be at least 1/2” BSP nominal
size and be in accordance with BS. 2879.
The central heating system should comply with the relevant standards on page 2.
Due to the compact nature of the boiler, the heat stored within the heat exchanger at the point of
shutdown of the burner must be dissipated into the water circuit in order to avoid overheating. To
allow pump operation after burner shutdown, the boiler control incorporates a pump overrun facility.
In order to make use of this, a pump must be controlled via the terminals inside the boiler.
When sizing pumps, reference should be made to hydraulic resistances given in Section 2.18, which
shows the boiler resistance against ow rates, to achieve the required temperature differential.
Flow rate using a 20°C temperature differential is 3.0 l/s (10.7 m³/hr) for each FHE-250
boiler/module.
The boilers MUST be installed in a closed loop system, it is the installers responsibility to ensure
adequate sized pressurisation units and expansion vessels are included for the system.
Note: With the boiler ring at maximum rate, the temperature differential should not be less than 20°C.
With the boiler ring at minimum rate, the temperature differential should not be greater than 35°C. Lower ow
rates generating higher temperature differentials will lead to poor system performance.
The lower the return temperature to the boiler, the higher the efciency. At return temperatures of 55°C and below,
the difference becomes marked because the water in the ue gases starts to condense, releasing its latent heat.
System designs should ensure the boiler minimum ow rates, as detailed in Section 5.2 - Boiler Specication,
are always maintained.
WARNING
If the water supply must be disconnected, the boilers must be turned off to prevent
accidental ue gas emission into the boiler room.
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