Part 7; Servicing; Sequence Of Operation; Servicing A Sequence Of Operation - Munchkin T50M Installing, Operating & Maintaining

PART 7. SERVICING
A. SEQUENCE OF OPERATION
1. When power is first applied to the control, the control display will read the outlet tempera-
ture. The control will initially run through a self-diagnostic routine and then go into its oper-
ating mode. If there is no call for heat, the System will go into an idle state.
2. If the thermostat is calling for heat, the control will apply power to the circulator pump. If the
control determines the water temperature is below the programmed set point value minus
the switching differential, the control will initiate a heating cycle.
3. The control then performs selected system diagnostic checks. If all checks are successfully
passed, a pre-purge cycle is initiated (the blower will be on maximum speed).
4. When the pre-purge period is complete, power is applied to the spark ignitor for approxi-
mately 6 seconds. Approximately 2 seconds later, we verify flame. If a flame is not verified
during the trial-for-ignition, the gas valve is immediately closed and the control will return to
step. After three trials, if a flame is not verified, the control will go into a lockout mode. If a
flame is confirmed, the control enters the heating mode. The fire rate will be based on the
proprietary algorithm.
5. When water temperature reaches the temperature set point value plus 10 degrees F (or if the
thermostat call-for-heat is satisfied), the gas valve is closed and the control enters a post-
purge state (the blower will be on maximum speed). NOTE: If the thermostat is still calling
for heat, the circulator pump will continue to run until the thermostat call for heat is satis-
fied.
6. When the post-purge is complete, the control enters an idle state while continuing to moni-
tor temperature and the state of other system devices. If a call-for-heat is received, the con-
trol will automatically return to step 2 in sequence and repeat the entire operating cycle.
During the idle state and heat state, if the control detects an improper operating state from external
devices, such as the high-limit switch, the red light on the control will illuminate an error code will
appear in the display.
B. MUNCHKIN TEMPORARY FAULT CONDITION
A Temporary Fault Condition may occur in the installation of the Munchkin. This condition may lead
to a lock out condition of the controller, which will need to be manually reset through the S4/Reset
button. These temporary codes will help the installer correct the problem before going into a lock
out condition, which will require a manual reset. Example: A temporary fault-code of E15 indicates
that the Air Pressure Switch is open when the fan is in the pre-purge function, when it should be
closed. This could occur if the clear hose, which is connected to the outlet of the fan is disconnect-
ed. This can be corrected by re-connecting the hose. Listed below are the Temporary Fault Codes.
E00 This code will appear if there is an overshoot of the high limit. The Temporary Fault Code will
be displayed only 50 seconds.
E13 This code will appear if the expected fan speed is lower then 70%. This will show on the dis-
play 10 seconds after the fan has started. The Temporary Fault code will only be displayed an
additional 50 seconds before going into lock out mode (F13).
Remedy – Check wiring to assure that the Fan is connected correctly.
E14 This code will appear if the expected fan speed is higher then 130%. This will show on the
display 10 seconds after fan is started. The Temporary Fault Code will only be displayed an
additional 50 seconds before going into lock mode (F14).
Remedy – Check wiring to assure that the Fan is connected correctly.
E15 This code will appear if the Air Pressure Switch is open when the fan is switched on in the
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SERVICING