District heating leakage protection

Domestic systems FB & FX OptiTight®

System FB OptiTight


System FB OptiTight®
Normally insulated buildings up to app. 250 m² with hot water storage.
System FX OptiTight®
Normally insulated buildings up to app. 250 m² with direct supply water heating, or app. 400 m² with hot water storage.

  • Forward and Return flow meters
  • Cutoff and non-return valves
  • Control Unit

Monitoring functions

Forward and Return flows are monitored continuously, compensating for volume and meter differences. If a preset flow difference limit is exceeded, leakage alarm is issued and the installation is cut off.

Seepage: OptiTight®
The patented OptiTight® mechanism employs individual control of the cut-off valves to test the installation tightness one or more times daily, whereby even minute seepage may be detected.

System Error:
The system checks the flow meters against each other, whereby meter blocks and occurring defects are immediately discovered.
Whenever a valve is closed - manually or by alarm - the system checks its tightness.
In case of component failure, System Alarm is issued, and the installation is cut off.

Supply Error:
The system monitors the mains supply and all internal supplies. If either of these fail, a Supply Error is issued. This may not cause a cutoff of the water supply.

systemdiagram FB OptiTight
1: Control Unit
3: Forward flow meter
5: Return cutoff valve
2: Forward cutoff valve
4: Return flow meter
6: Non-return valve

Alarm Functions

On leakage and system errors, System FB/FX will cut off the installation, issue visual and audible alarms, and activate the alarm relay.
Supply errors are reported via the alarm relay, and possibly also visibly and audibly.


Controls and Indicators:
Mains, Forward, Return, Valve and State indicators, buzzer.
Buttons for manual valve control and alarm acknowledge.

Leakage monitor:
Base measuring period 210 sec.
Truncation at 32 litres forward volume.
Tolerable flow difference Forward-Return in measuring period 5 ltr.

Activation: 1, 2, 3, or 4 times daily.
Base time 02:00 + 24 / 2*12 / 3*8 or 4*6 hours. May be delayed up to 1 hour if consumption is high.
Duration: 7.5, 15, 30, or 60 minutes.
Sensitivity up to 3 liters/hour.

Mains connection
230V 50Hz L/N/PE via external key switch. Power consumption max 20VA.


Liquid Sensor Attachment:
System FB/FX accommodates via interface ILS-C a Liquid Sensor type LS-X, whereby the system offers point protection of a particularly sensitive area so that the installation may be cut off on Liquid Sensor alarm if desired.

By attachment of an external SMS-alarm to the alarm relay output, system FB/FX can ship a text message to a selected mobile phone number.
System Capacity and pressure drop Dimensions
Nom. Cap.
Qn (m³/h)
 ΣΔp@Qn Equivalent
Kvs (m³/h)
(mwc) (kPa) Flow meter Cutoff valve Non-return valve
FB OptiTight 1,5 4,7 47 2,2 ½" x 165 mm ½" x 55 mm ½" x 47 mm
FX OptiTight 2,5 4,9 49 3,6 ¾" x 195 mm ¾" x 76 mm ¾" x 56 mm

EAN/UPC ordering codes here

Download System FB/FX data sheet in pdf-format

Download pamphlet Domestic Leakage Protection in pdf-format