Rinnai FUA-E, Service Manual, Page: 32 / 67

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E. Thermal Fuse (Overheat) Circuit.
First locate the Overheat circuit. It is made up of red wires making a loop through the
unit, including a number of thermal fuses, and the overheat bi-metal switch. Along the
right-hand side of the unit the red wires can be seen running down the side of the unit
from the bi metal switch. One of these red wires has a connector approximately in front
of the transformer (Connector A5 from wiring diagram.)
With the unit electrically isolated unplug this connection A5. Unplug connector C from
the PCB. Put multimeter lead into the red wire from connector C and the other lead into
the half of Connector A5 that is attached to the bimetal switch. Measure the resistance
through this overheat circuit.
Resistance should be less than 1 Ohm.
If the resistance is greater than 1 Ohm test each individual sensor to find which one is
faulty and replace it AFTER checking the heater for damage. Check that the gas type
and combustion dip switch settings are correct. Confirm gas pressure when the unit is
operating again.
F. Gas Filter.
There is an inline gas filter in the inlet pipework connection. If the gas pressure will not
achieve the correct level, and the inlet pressure is correct (20mbar) then drop the gas
connection out to see whether there is a blockage in the filter.
Diagnostic Checks