STP SERIES Install, Operation, and Maintenance Manual
SECTION 5: TROUBLESHOOTING
Rev-1
Diversified Heat Transfer, Inc.
•
439 Main Road, Route 202
•
Towaco, New Jersey 07082
Page
77
of
97
STP Manual
PHONE: 800-221-1522
•
WEBSITE: www.dhtnet.com
09/11/2019
thermocouple or Aquastat is installed and functioning correctly.
Repair or replace it if needed.
Excessive or
insufficient
boiler water
being returned
from the unit.
1. The water return piping has not been
installed properly to allow the water
return; boiler water return line is
restricted; or the return check valve is
leaking or has failed.
2. There is water leakage in the heat
exchanger.
1. Rearrange the boiler water return piping and inspect the valve for
proper drainage. Also check to make sure there is no restriction in
the water return line. Replace the check valve if it is leaking or has
failed.
2. Shut off the isolation valves on inlet and outlet of the unit and check
to verify the presence of leakage. Disassemble, inspect, repair (if
possible), or replace the heat exchanger and reassemble the unit.
Unit is not
heating the
domestic water
and control
valve(s) or VFD
pump(s) is
closed.
1. There is no power supply to control valve
or optional VFD pump.
2. There is no signal from controller to valve
or VFD pump.
1. Open the valve or pump cover and check to make sure 24VAC
power is present at valve terminals. Troubleshoot panel to restore
power if it is not present.
2. Open the valve or pump cover, and check 4-20mA control signal is
present at terminals (4-20mA converted to 2-10VDC for pump).
Troubleshoot panel to restore proper signal to control valve or VFD
pump if it malfunctions. Also check control valve dip switches or
pump controller settings as shown in Section 6.4.
Temperature
and Pressure or
pressure only
relief valve
“pops.”
1. Control Valve or VFD pump does not
close properly.
2. Improperly sized or disconnected
expansion tank in closed loop piping
system.
3. Inadequate water hammer arrestors.
4. System/incoming water pressure is too
high.
5. Relief valve is faulty.
6. Over temperature settings in PID
controller or Aquastat not properly set or
1. See the adjustment and testing instructions contained in Section
3.11 for the specific temperature control system installed on the
unit. Also, check to ensure that the thermocouple is installed and
functioning correctly. Repair or replace it if needed. Replace the
control valve and/or actuator if necessary. Refer to Section 4.6 for
replacement instructions.
2. Install the properly sized expansion tank in the closed loop piping
system as shown in Installation and Piping drawings in Section 6.3.
3. In order to avoid any shock waves, install water hammer
arrestors/shock absorbers in the hot and cold water systems as
needed.
4. Bring the system water pressure below the relief valve setting.
5. Inspect and adjust or replace the relief valve if it has failed. Contact
DHT representative for replacement.
6. Check and readjust as necessary. Replace the defective parts as
necessary. Refer to adjustment instructions contained in Section
