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TROUBLESHOOTING GUIDE
TROUBLESHOOTING GUIDE
Modulating Room Temperature (MRT, MRT-PRO or MRT-EXPERT) Controls
Portions reproduced with permission from Maxitrol
®
Company
Symptom
Possible Cause
Field Test
Remedy
1. Install properly.
1. If proper resistance values
are not observed, replace
modulator head or repair
wiring.
2. Clean or replace plunger if
necessary.
3. Replace diaphragm if
ruptured.
1. Provide 24V AC to amplifi er.
2. If proper resistance values
are not observed, replace
the modulator head or repair
wiring.
3. If power source and
modulator coil check out
(items 5 & 6) but proper
modulating voltages cannot
be obtained, then amplifi er
may be assumed at fault.
Install replacement amplifi er.
4. Consult factory.
1. Adjust to proper low fi re.
2. If greater than 1.5" negative
pressure, check equipment
for clogged fi lters and other
inlet air restrictions. For other
solutions, consult factory.
1a. Replace Sensors if reading is
incorrect or correct wiring.
1b. Change to correct setpoint.
1c. Change to correct setpoint.
1. Change to correct setpoints.
A. No Gas Flow with
DO-2 on UC-01
energized.
B. Continuous Low
Fire (Electronics
OK).
C. Continuous Low
Fire (Electronics
Problem).
D. Incorrect
Low Fire.
E. Continuous
Minimum
Discharge Air
Temperature.
F. Incorrect
Maximum
or Minimum
Discharge Air
Temperature.
Control circuits external to MRT Controls can cause burner malfunction.
Always check manual valve to be certain gas is on, and check limit controls for normal operation.
1. Arrow on side of valve
should point in direction
of gas fl ow.
1. Remove wires connected
to amplifi er terminals 5 & 6
and measure resistance.
MR212 (60-80 ohms),
M611 (45-55 ohms).
2. Inspect - plunger should be
installed to operate freely in
solenoid sleeve.
3. Disassemble valve for
inspection of internal parts.
1. Check for 24V AC at
amplifi er terminals 7 & 8.
2. Measure resistance per
item B1.
3. Check for 0 – 10 VDC input
signal from Unit Control
Module (UC-01) at terminals
1 & 2. Check for 0 – 20 VDC
output signal to gas valve at
terminals 5 & 6.
4. Check voltage on AO-1.
1. See Valve Adjustments
Section X.
2. Close main gas supply and
measure manifold pressure
with blower operating.
Should be less than 1.5" w.c.
negative pressure.
1a. Check Outside Air Sensor
(TS-01),Space Temperature
Sensor (TS-02) and Discharge
Air Sensor (TS-03) for correct
readings. See Thermistor curve.
1b. Check Space Temperature
Sensor (TS-02) and/or Unit
Enabled Poteniometer (MP-
15) setpoint.
1c. Check Heating Occupied
and/or Unoccupied setpoint.
1. Install a BACview 6 or PC.
1. Valve improperly
installed.
1. Open circuit in
modulator coil.
2. Plunger missing,
jammed or improperly
installed.
3. Ruptured main or
balancing diaphragm.
1. No voltage to the
amplifi er.
2. Short in modulator
coil circuit.
3. Faulty amplifi er (RE-26).
4. No output voltage on
UC-01.
1. Incorrect by-pass metering
valve adjustment.
2. Excessive negative
burner pressure.
1. Incorrect room
temperature.
1. Maximum or minimum
heating discharge
temperature setpoint
not set correctly.
(Refer to Digital Control System User Manual for additional troubleshooting suggestions)
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