Plumbing Systems
Fröling Heizkessel- und Behälterbau Ges.m.b.H, Industriestrasse 12, A-4710 Grieskirchen Page 51
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5.6 Return temperature control (Only for the model 80/100)
If the hot water return is below the minimum return temperature-usually
during cold start-up or when charging a storage tank, some of the hot water
must be mixed into the return flow. The model 80/100’s boiler control has this
function and must be utilized in order to prevent shortened boiler life and loss
of warranty coverage.
Risk of dropping flue gas temperature below the dew point / condensation formation if
operated without return temperature control
Condensation water forms an aggressive condensate when combined with combustion
residue, leading to damage of the boiler
At low outside temperature condensation water may freeze at chimney outlet and will lead
to insufficient chimney draft with restrictions to boiler power including possibility of system
break down
We recommend that you use a return temperature control.
❒ The minimum return temperature is 140°F (60°C). We recommend fitting a 3-way
mixing valve including valve motor (pulse control) and a temperature sensor.
Automatic closed loop control for return temperature is provided within the boiler
control system.
5.7 Supply and Return Connections
Please pay attention to connection labeling on back of boiler. For P4 Pellet 8-
38 models the supply connection is the lower connection and on the P4 Pellet
48-100 models the supply connection is the upper connection. Only the P4
Pellet 80/100 will need return temperature control.
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