19
6.5
Pressure relief valve
The S-CB
+
400 & 550 boiler has no internal pressure relief valve. This should be fitted in the flow line of the system
near the boiler. When having multiple boilers, each boiler must have its own pressure relief valve. We advise to install
service valves, so the boiler can be isolated from the heating system, when maintenance or service needs to be
carried out. Make sure the pressure relief valve is mounted between the boiler and the service valves. The pressure
relief valve must always be installed in such a way that it cannot be isolated from the boiler by a valve.
The specifications and size of the relief valve should be determined by the installer and must comply with all appli-
cable standards and regulations.
6.6
Bypass
The boiler has no internal bypass. If many thermostatic valves are being used, the system should have a bypass to
allow adequate flow in case all the thermostatic valves are closed.
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 sections must be
insulated and/or protected with the help of a tracing.
Installing the boiler flow circuit in series with the heating system is possible, but not preferable. We advise
to install a low loss header behind the boiler, so flow restrictions on the installation side can never influence
the boiler flow. Using a low loss header prevents both before mentioned boiler threats (frost and too many
thermostatic valves) and guarantees free boiler flow.
6.7
Pump functionality
The pump capacity must be determined for each project. The boiler pump (P1) can be controlled directly by connect-
ing it to the internal relay.
The boiler pump must be controlled by the boiler controller. If, for any reason, an external pump control is
applied
without written approval of Strebel
, the complete warranty on the boiler and all supplied parts will
become invalid.
A safety switch for the pump motor must be installed externally (when needed) and is not included
in the boiler supplies.
We supply a 230 VAC signal for controlling the external relays that will switch the system pump (P3) or the calorifier
pump (P2).
Do not use these connections as a supply, always use an external relay for controlling these
pumps.
6.8
Frost protection
The boiler has a built-in frost protection, that is automatically activating the central heating pump when the boiler
return (water) temperature drops below the 5°C (programmable). When the boiler return temperature drops below
the 3°C (programmable), the burner is also ignited. The pump and/or burner will shut down as soon as the return
temperature has reached the 10°C (programmable). The mentioned temperatures are related to the temperatures
measured by the RETURN sensor of the boiler. This frost protection function will not fire up the boiler in case of a
“general blocking” of the burner demand.
NOTICE: T
his “Frost Protection” function is only useable for the boiler and not for the whole central heating system.
Because it concerns a programmable setting, a boiler damaged by frost is not covered under warranty.
