35
Test or Condition: Result: Action Taken:
Start - Disconnect sensor
leads from electronic control
module and measure
resistance of sensor(s) with
ohmmeter
Is resistance between 700 and
30K ohms (see page 38)?
YES↓ NO→
Sensor(s) may be shortened
or open. Check for loose,
broken or shorted wires.
Replace sensing bulb(s) if
necessary.
Sensors O.K. Disconnect
ECO leads and measure
resistance with ohmmeter
Is water temperature greater
than 210°F (99°C) and ECO
resistance less than 10 ohms
(shorted)?
YES→ NO↓
Replace sensing bulb with
ECO limit and check out
balance of system.
Disconnect potentiometer
leads from electronic control
module. Measure resistance
of potentiometer with
ohmmeter.
Is resistance greater than
4800 ohms at minimum
temperature setting (checks
for short)?
YES↓ NO→
Replace electronic control
module. Reconnect all leads
and check out system
Potentiometer O.K. Replace electronic control
module. Reconnect all leads
and check out system
If water temperature is too cold or heater does not come on, proceed as
follows:
Test or Condition: Result: Action Taken:
Start: Check voltage at 24-volt
terminals of electronic control
module of thermostat board.
Is voltage between 21.5 and
28.5 VAC?
YES↓ NO→
Check power supply,
transformer. Correct as
necessary.
Are main burners operating or
is pilot trying to light
(sparking)?
YES↓ NO→
Check for voltage at N.O.
thermostat terminals (terminal
to meter to ground). Is voltage
between 21.5 and 28.5 VAC?
YES↓ NO→
Thermostat relay is not
closing. Check thermostat
setting. Refer to thermostat
troubleshooting below.
Troubleshooting Procedure for Electronic Thermostat (continued)-
If water temperature is too cold or heater does not come on, proceed as
follows:
Index