– 19 –
1. Clean, replace valve and/or
seat if necessary.
2. Clean, or if necessary,
replace plunger.
1. If readings are incorrect,
replace Outside Air
Temperature Sensor (TS-01),
Space Temperature Sensor
(TS-02) or Discharge Air
Temperature Sensor (TS-03)
or repair wiring.
1. Increase inlet pressure
if possible or change to
larger valve. Consult factory
about possibility of using
special spring to reduce
pressure drop on selected
installations.
2. See Valve Adjustments
-Section X.
1. If readings are incorrect,
replace Space Temperature
Sensor (TS-02) or Discharge
Air Temperature Sensor
(TS-03) or repair wiring.
1. If proper resistances are not
observed, replace modulator
head or repair wiring.
2. Correct wiring if short is
found.
1. If desired temperature is
not reached, increase
Maximum Heating Discharge
Temperature Setpoint.
2. If desired Space Temperature
is not reached, increase
Minimum Heating Discharge
Setpoint.
3a. Change to correct setpoint.
3b. Change to correct setpoint.
4. If desired Space Temper-
ature is not reached with
heater at high
fi
re, it may be
undersized. Consult Factory.
TROUBLESHOOTING GUIDE
TROUBLESHOOTING GUIDE
Modulating Room Temperature (MRT, MRT-PRO or MRT-EXPERT) Controls
continued
Portions reproduced with permission from Maxitrol
®
Company
Symptom
Possible Cause
Field Test
Remedy
1. Foreign material
holding valve open.
2. Plunger jammed.
1. Open circuit in Outside
Air Temperature
Sensor (TS-01), Space
Temperature Sensor
(TS-02) or Discharge
Air Temperature Sensor
(TS-03)
1. Inlet pressure too low.
2. Incorrect outlet
pressure adjustment.
1. Open circuit in Space
Temperature Sensor
(TS-02) or Discharge
Air Temperature Sensor
(TS-03).
1. Short in modulator
coil circuit.
2. Short circuit between
ampli
fi
er and modulator
valve.
1. Incorrect Maximum
Heating Discharge
Temperature Setpoint.
2. Incorrect Minimum
Heating Discharge
Temperature Setpoint.
3. Incorrect space setpoint.
4. Insuf
fi
cient burner
capacity.
G. Continuous High
Fire (Electronics
OK).
H. Continuous High
Fire (Electronic
problem).
I. Incorrect
High
Fire.
J. Continuous
Maximum
Discharge Air
Temperature.
K. Burned out
Transformer.
No Voltage to
Ampli
fi
er.
L. Incorrect Space
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. Remove bottom plate and
inspect valve and seat.
2. Inspect - plunger should be
smooth and clean and operate
freely in solenoid sleeve.
1. Measure resistance per
Thermistor Curve.
1. Read inlet pressure at
valve, using a manometer
with heater operating at full
fi
re. Pressure should be at
least equal to the sum of:
outlet pressure setting and
pressure drop of the valve
plus 1.0" w.c.
2. Read outlet pressure using
manometer and compare
with the pressure stated on
the speci
fi
cation plate.
1. Measure resistance per
Thermistor Curve.
1. Measure resistance per
item B1.
2. Inspect wiring.
1. Check to see if heater is
delivering at Maximum
Heating Temperature
Discharge Setpoint.
2. Check to see if heater
is delivering at Minimum
Discharge Setpoint.
3a. Check Unit Enable
Potentiometer (MP-15)
Setpoint.
3b. Check Heating Occupied
and/or Unoccupied setpoint.
4. Check to see if heater is
operating at high
fi
re.
(Refer to Digital Control System User Manual for additional troubleshooting suggestions)
