AERCO SWDW68 U-Tube Double-Wall Heaters w/ECS - Manual (Page 52)

HE-
111 − TROUBLESHOOTING
Rev B Mar 2013 7-10
Table 7-3 TROUBLESHOOTING – ELECTRONIC CONTROL SYSTEM
NO. FAULT INDICATION PROBABLE CAUSE CORRECTIVE ACTION
T18 Over-temperature alarm
occurs repeatedly.
NOTE
Audible alarms will be
generated if the Hot Water
Output temperature sensor is
open. Erroneous temperature
readings will be displayed if
sensor is shorted.
1. Over-temperature Switch is not
set properly.
2. Open or shorted Hot Water
Outlet temperature sensor
(thermocouple) is connected to
the Over-temperature Switch.
3. Over-temperature Switch is
defective.
1. Refer to Chapter 4 and check the current setting of the Over-
temperature Switch. Readjust as necessary.
2. Check thermocouple connections between Hot Water Outlet sensor
connector plug and TB-1 terminal leads 111 (+) and 112 (-). If
connections are secure, replace the Dual-temperature Sensor.
3. Replace the Over-temperature Switch.
T19 Over-temperature alarm
condition cannot be cleared.
Over-temperature Switch
displays erroneous
temperature readings
1. Shorted Hot Water Output
temperature sensor.
2. Defective Over-temperature
Switch
3. A “No-Flow” condition is
causing a gradual buildup of
heat in the vessel water.
4. External recirculation pump
has shut off or has failed.
5. Over-temperature Switch
setting is too low.
6. Packing nut is too tight.
7. Over-temperature Solenoid
Valve is leaking or open.
1. Replace Hot Water Output Temperature Sensor.
2. Replace Over-temperature Switch.
3. Open heat exchanger Hot Water Outlet to see if fault clears. If there
is no flow through the heat exchanger, see Probable Cause 4.
4. Check pump to ensure that it is turned on and functioning properly.
Also, check for blockage in the incoming flow.
5. Refer to Chapter 4 and check the current setting of the Over-
temperature Switch. Readjust as necessary.
6. Loosen the packing nut and re-tighten it avoiding the use of
excessive force.
7. Inspect the solenoid valve for evidence of leaks. If leaks are
detected, replace the solenoid valve.