LAARS NeoTherm NTV (Sizes 399-850 MBTU/h) - Service Manual - Manual (Page 33)

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Service Manual - NeoTherm 500
Testing the Flow Switch
The flow switch uses a set of paddles to sense water
flowing through the system. See Fig. B9-2. When
water is flowing, the switch is normally closed (N.C.).
If the water flow stops, the switch opens. After a “no
flow” condition, the switch resets itself immediately
and automatically.
Shut off power to the boiler, and remove the cover on
the switch. Use a volt-ohmmeter to test the continu-
ity through the switch. With no water flow and the
paddles in the “relaxed” position (standing upright),
the switch should be open.
Note - There is a seal at the base of the paddle as-
sembly. If this seal fails, it can allow water to leak
into the connection box. From there, the water can
flow through conduits to other parts of the control
system in the Magna-Therm unit.
If it is necessary to replace the flow switch, see Sec-
tion B10 for instructions.
Fig. B9-1 – Typical flow switch installation
B9
Fig. B9-3 – Flow switch with cover removed Fig. B9-2 - Metal paddles used to detect water flow
(typical)