American Water Heater GAS-FIRED COMMERCIAL WATER HEATER - Manual (Page 37)

37
thermostat board, and the
heater operates if this wire is
jumpered to the “COM”
terminal above it, then make
the following checks to the
thermostat circuit. This
procedure also applies if the
burners cycle on for short
periods, but the water
temperature seems low. measure resistance of
sensor(s) with ohmmeter. Is
resistance between 700 and
30K ohms (see page 38)?
Measure water temperature
from tank for an approximate
correlation with the table.
YES
↓ NO→
wires for loose, broken, or
shorted wires. Replace
sensing bulb or wire harness.
If necessary.
Sensors O.K. Check remote
potentiometer. Disconnect potentiometer
leads from electronic control
module. Measure resistance
of potentiometer with
ohmmeter. Is resistance
greater than 4800 ohms at the
minimum temperature setting
and less than 50 ohms at the
maximum temperature setting
(checks for open or shorts)?
YES
↓ NO→
Replace potentiometer.
Reconnect all leads and
check out system.
Potentiometer O.K. Replace electronic control
module. Reconnect all leads
and check out system.
Temperature Control Checkout
Set the L8104 above water temperature (See page 27) and observe system
through one (1) complete cycle. Make sure system operates as desired.
To check the thermistor or thermistor/ECO assembly, compare it’s resistance
as measured by an ohmmeter to the water temperature as measured by an
accurate thermometer. Thermistor resistance increases as the temperature
decreases. The tables below show the correct sensor resistance at various
temperatures.
Index