System Feed/Return Pipes; System Fill/Drain Pipe; Pipes, Expansion Vessel And Safety Valves; Recirculation Pump - Ferroli PREXTHERM RSW Series Instruction For Use, Installation And Assembly

PREXTHERM RSW N
- Corrosion on the water side
Corrosion of the metal surfaces on the water side of the boiler is caused by the dissolution of iron into its ions. The presence of dissolved
gases, particularly oxygen and carbon dioxide, plays an important role in this process. Softened and/or demineralized water provides pro-
tection against deposits, but not against corrosion. The water must therefore be treated with corrosion inhibitors.

5.5.2 System feed/return pipes

The dimensions of the feed and return pipes for each boiler model are indicated on the DIMENSIONS table. Make sure the system has a
sufficient number of vent openings.
The boiler fittings must not support the weight of the connection pipes to the system. Appropriate supports must be installed for this purpose.

5.5.3 System fill/drain pipe

For filling and draining the boiler, a cock can be connected to fitting T4 on the back (see DIMENSIONS, Fig. 3).

5.5.4 Pipes, expansion vessel and safety valves

PREXTHERM RSW N boilers are suitable for operation with forced water circulation, with the expansion vessel open or closed. An expan-
sion vessel is always required to compensate for the increase in water volume due to heating. In the first case, the height of the hydrostatic
column must be at least 3 meters above the boiler body. Its capacity must be sufficient to contain the increase in volume of all water in the
system, between the surface of the water in the vessel and the overflow pipe. Tall, narrow vessels are preferable, as they ensure minimum
contact between the water surface and the air, thus reducing evaporation. In the second case, the capacity of the closed expansion vessel
must be calculated considering:
- the total volume of water contained in the system
- the maximum operating pressure of the system
- the maximum operating pressure of the expansion vessel
- the initial pre-charge pressure of the expansion vessel
- the boiler's maximum operating temperature (the maximum temperature on the thermostat fitted on the panel is 90ºC; use 100ºC to
perform this calculation).
The expansion pipe connects the expansion vessel to the system. This pipe will start at the T3 fitting (see the Dimensions table), and must
not be fitted with on-off valves. At fitting T3, or within 0.5 m of the first flange on the outlet pipe, install a safety valve suitable for the capacity
of the boiler and in compliance with current local standards. No type of shut-off device may be installed between the boiler and the safety
valves, and these valves should be set to operate when the maximum permitted operating pressure is exceeded.

5.5.5 Recirculation pump

Condensation ºof the water vapor contained in the flue gas leaving the boiler (conden-
sate) occurs when the return water temperature is below 50ºC. This is significant,
particularly when the boiler is turned on in the morning after being off all night. Con-
densate is acidic and corrosive, and will damage the metal plating on the boiler over
time. It is therefore advisable to install a recirculation pump with an anti-condensa-
tion feature, to be fitted between the feed and return fittings, upstream of any mixing
valve. While the system is operating, the pump must ensure a flow-rate of 20 to 30%
of the total. The (anti-condensation) recirculation pump is controlled using the
Low-Temperature Thermostat Panel (optional). The bulb for the corresponding ther-
mostat must be fitted at the return (using a sheath that must be added by the installer
of that pipe).

5.6 Adjusting the front door

For PREXTHERM RSW models 1250N÷1890N the door is hinged, fastened and
reversed as regards the direction of opening as shown in Fig. 10. The following
operations are required:
- The door is supplied with four equal brackets (pos. 3) and hinges.
- To establish the direction of opening, RIGHT or LEFT, unscrew the nut (pos. 7), unscrew and remove the R or L nut (pos. 6), depending
on which side the door opens from.
- Height adjustment of the door is performed using the nut (pos. 2); after having completed the adjustments tighten the dowels (pos. 1).
- Longitudinal adjustment is performed using the screw (pos. 8).
cod. 3545453/0 - 06/2019
fig. 9
35
EN