Rinnai FUA-E, Service Manual

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Diagnostic Checks
The rest of the circuit, including the valve heaters should be about 270 Ohms. Measure
it by unconnecting the connector to the top heater and the connector to the hot water
outlet valve heater and measure resistance through the sides of the connectors that lead
to the valve heaters. Through one side there will be no resistance, through the other side
there will be about 270 Ohms.
The entire anti frost heater system is done as a kit, so the easiest check is to see if they
heat up when the sensor is closed. If not, replace the system. There will be 240 Vac
through the heaters if the system is working so take care.
U. Frost Sensing Switch
The frost sensing switch is located at the top left of the heat exchanger. It is a black, top
hat style bi-metal switch. It is a normally open contact so to prove it is working it must be
cooled to about 5°C. At this temperature the resistance in the switch can be tested, it
should be less than 1 Ohm.
V. Check Flue
If there are combustion problems they could be due to the flue. Is the flue too long? The
maximum flue run is 6.5m, less 0.5m per bend, to a maximum of 3 bends. For flue
extensions a condensate trap is required If there is a condensate trap installed, be sure
it is the right way up.
If the flue gases recirculate back into the combustion air the unit will shake like it is going
to come off the wall, and makes a similar noise to the rumble strips on the side of
motorways. This can be due to the terminal being in a sheltered place or a corner, or the
flue not being put together right..
Diagnostic Checks