Rinnai REU-16 Service Manual page 35

Diagnostic Checks
Hot Water Outgoing Thermistor
This thermistor is located at the bottom left of the water heater where the water exits the
water heater.
Combustion Air Thermistor
This thermistor is located next to the controller connection point on the right hand side of
the unit above the pcb. It is at the end of the two yellow leads.
L. Check Non Return Valves and Mixers in System
Non Return valves and mixing valves occasionally have a tendency to pass cold water,
especially if there is a mismatch of pressures. The easiest way to check for this is to
isolate the valves on the water heater and turn on all the hot taps, one at a time. If there
is a flow of water (besides the initial flow which is the pipework draining down) then there
is a mixer valve or non return valve in the system passing.
There is another way to check non mixers and non return valves, especially in situations
where the temperature varies or is only warm. Isolate the hot water outlet somewhere
between the water heater and the first draw off. If there is a circulating loop (secondary
return) isolate this as well. Now if you open the pressure relief valve of the water heater
or a drain off point somewhere between the hot water outlet and the valve that has been
isolated the only water that will travel through the water heater will be mains water at
fairly constant temperature. Measure the outlet temperature at this drain off point. If the
temperature is constant, and correct for the setpoint, then the water heater is working as
it should and you need to find the mixing valve or non return valve that is faulty.
It is important to make sure that the secondary return has a non return valve installed
after the pump.
M. Air Locks in the Heat Exchanger.
Upon commissioning or cleaning the filters, if the water heater is the highest point of the
system the heat exchanger may experience an air lock.
To clear it, isolate the hot water outlet and open the pressure relief. The incoming mains
should push the air lock out and the unit will fire.
To avoid air locks when cleaning the filter follow the filter replacement steps under
section R.
N. Check Power Supply to the unit.
To make sure there is power to the unit make sure all the electrical isolators are On and
the fuses are okay. With your meter check for 240Vac on the connection plug I of the
pcb. Do this with the connector plugged in, and the unit in standby mode (power on,
water off.) Stick the meter leads in the blue and brown plug.
If there is no power at this point you must find where the connection has been lost up to
the unit.
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