Service manual
06/2010
thermister cable 1329 for continuity on the two yellow wires. If either wire shows a break, replace the
cable 1329. Otherwise, replace the T-mid thermister 2008 per SM500-08.
Single Red flash
Indicates that the T-out thermister has failed. The heater will substitute a calculated (model) T-out,
based on T-mid, and continue to operate. At a constant water flow the temperature output will
remain constant. Over the operating water flow range, normally, this approximation will be within
3F. If the variation is noticeable and improvement is needed, proceed with the checkout in section
4.3 and, if necessary, replace the T-out thermister per SM500-09. Otherwise, the unit can continue
to operate.
Two Red flashes
Indicates that the T-in thermister has failed. The heater will assume 70F for T-in and continue to
operate. As long as incoming water temperature is near 70F operation will be normal. However, as
inlet water temperature deviates from 70F the unit will be slower reaching the set temperature and
eventually, the unit will be unable to reach the set temperature. If the variation is noticeable and
improvement is needed, proceed with the checkout in section 4.3 and, if necessary, replace the T-in
thermister per SM500-07. Otherwise, the unit can continue to operate.
Three Red flashes
T-mid is not in the operating range of 30 - 160F. The unit continues to operate using the measured
T-mid, however, the operation is likely affected since the T-out model will be much different and the
unit will not be able to reach the set temperature at many or all water flows. If the variation is
noticeable and improvement is needed then proceed with the checkout in section 4.3 and, if
necessary, replace the T-mid thermister per SM500-08. Otherwise, the unit can continue to operate.
Four Red flashes
T-out is not in the operating range of 30 - 180F. The unit continues to operate using the measured
T-out, however, the operation is likely affected since the real heat exchanger outlet temperature will
be much different and the unit will not be able to reach the set temperature at many or all water
flows. If the variation is noticeable and improvement is needed then proceed with the checkout in
section 4.3 and, if necessary, replace the T-out thermister per SM500-09. Otherwise, the unit can
continue to operate. Temporary, improved operation may be obtained by disconnecting the T-out
thermister at the 2-pin connector (see ‘Single Red Flash’).
Five Red flashes
T-in is not in the operating range of 30 - 110F. The unit continues to operate using the measured T-
in, however, the operation is likely affected since the real heat exchanger inlet temperature will be
much different and the unit will not be able to reach the set temperature at many or all water flows. If
the variation is noticeable and improvement is needed then proceed with the checkout in section 4.3
and, if necessary, replace the T-in thermister per SM500-07. Otherwise, the unit can continue to
operate. Temporary, improved operation may be obtained by disconnecting the T-in thermister at the
2-pin connector (see ‘2 Red Flashes’).
Six Red flashes
T-in is larger than T-mid and T-mid is larger than T-out. This indicates that the water is flowing
through the unit backwards. Check the water inlet and outlet connections because they must be
reversed. The water inlet is the upper connection and the water outlet is the lower connection. This
is the opposite of RV hot water tanks.
Seven Red flashes
The direct spark ignition (DSI) has timed out (after two 3.5 second ignition attempts) and the DSI
board 3158 has locked out. After 45 seconds the software on circuit board 1841-RV will reset the
DSI board and the ignition sequence will be repeated. The DSI can also be reset by turning off water
a few seconds and then on. The red LED will continue to flash even though the unit is now
operating. The red LED can be reset by cycling the power OFF, then ON. If the unit frequently locks
out refer to section 3.6 ‘Green LED flashes, but no ignition (no igniter sparks, no gas flow, no odor).