Strebel S-FX 125, Installation Operating & Maintenance Manual

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6.7 Expansion Vessel
The capacity of the expansion vessel must be selected and based on the capacity of the central heating system
and the static pressure. Suggested is to fit the expansion vessel in the return pipe of the central heating system.
6.8 Pressure relief valve
The S-FX boiler has no internal pressure relief valve, it is required to be installed as close to the boiler on the flow
pipe of the heating system. When having cascaded boilers, each boiler requires to have its own pressure relief
valve. It is recommended to install isolation valves on the flow and return pipework, so the boiler can be isolated
from the heating system, when needed. Make sure that the pressure relief valve is mounted between the boiler
and the isolation valves.
Alternatively, there is a connection on the S-FX boilers flow pipe just before it connects to the system which is
plugged off. This is primarily used for any BMS temperature sensor require but can be used to connect a safety
valve. But due to the size of the connection, NABIC FIG 500 high lift valves will be required:
- S-
FX 70 & 125 = ½” FBSP Connection.
- S-
FX 220 = ¾” FBSP Connection.
- S-
FX 320 = 1” FBSP Connection.
The specifications and size of the relief valve should be determined by the installer and must comply with all
applicable regulations and boiler capacity.
6.9 NON-Return Flap.
All S-FX boilers have a non-return valve installed on the air pipe just before the internal combustion fan. This gives
protection of flue gas recirculation, but it should not be classed as a prevention of flue gas recirculation as it is not
a non-return valve.
6.10 Bypass
The boiler has no internal bypass. When many thermostatic valves are being used, the system should have a by-
pass to allow an adequate flow when all thermostatic valves are closed.
Instead of a bypass also a low-loss header or a SMH Boiler Guard can be used for this function.
The boiler flow will also be influenced when a pipe of the heating system is frozen / blocked. Make sure all heating
pipes are free from the risk of frost. If there is the risk of freezing of the heating system, all the pipe section must
be insulated and/or protected with the help of a tracing.
6.11 Frost protection
The boiler has a built-in frost protection that is automatically activating the S-FX boiler and connected heating
pumps when the boiler supply / flow (water) temperature drops below 6 °C.
This frost protection function will not fire up the boiler if the power supply or gas supply has been turned off. If
necessary, for system protection use a suitable antifreeze liquid as listed within chapter 6.5.
NOTICE: A boiler damaged by frost is not covered under warranty.
6.12 Automatic Filling System / Pressurisation Units.
When using an automatic water refill system some precautions should be taken (fresh water is bringing fresh
oxygen into the system), like installing a water meter to measure and evaluate the total water volume that is added
to the system. This to detect and eliminate any water leakage as soon as possible. When an automatic water refill
system is used, some form of logging should take place to prevent continuously filling of the system with large
amounts of oxygenated fresh water. This can happen when a leak in the system is not detected and the total
added water amount is not being logged.
6.13 Water pressure
The installation should be designed and built to conform to all applicable regulations and standards, including the
right safety valves. IMPORTANT: Always keep the pressure in the boiler lower than the value at which its safety
relief valve opens.
Switch
A water pressure switch has been built into the boiler. With this switch, the minimum water pressure in the boiler
is 0.5 bar. The normal water pressure is supposed to be between 1.5 and 2.0 bar.
The pressure sensor will stop the boiler from firing when the water pressure drops below 0.5 bar, and start the
boiler firing again when the water pressure reaches above 1.0 bar.