© Danfoss | 2023.04| 25
LGB53541
Termix VMTD-IV MIX - 5 Series DS Fully insulated
Troubleshooting
Area of operation
Problem
Possible cause
Solution
Instantaneous water heater,
thermostatic
Incorrect DHW
temperature
The strainer in the supply
or return line is clogged up
Clean the strainer
Too high DHW flow rate
Check the dimensioning of DHW load, actual flow
temperature and differential pressure
Defective mixer tap
Check if the mixer tap is defective and if so, replace
Defective or blocked check
valve on the circulation valve
Check and replace if defective
Incorrect set-point on the
DHW controller
Set the DHW controller’s thermostat to the correct value
according to the section “Adjustments, domestic hot water”
Defective DHW controller
1) Check the sensor: Remove the sensor head from
the valve. If the DHW temperature then increases,
replace the sensor
2) If the DHW temperature does not increase,
replace the entire valve
Plate heat exchanger has calcified Replace the heat exchanger
Domestic hot water
flow is too low
The filter on the cold water supply
is clogged up
Clean the filter
Plate heat exchanger has calcified Replace the heat exchanger
Long wait for
domestic hot water
Idle temperature is too low
Set the DHW controller’s thermostat to the correct value
according to the section “Adjustments, domestic hot water”
DHW circulation temperature
has been set too low
Set the thermostat higher or turn up the DHW circulation
pump
Direct heating, thermostatic
Incorrect flow
temperature for
space heating
The strainer in the supply
or return line is clogged up
Clean the strainer
Incorrect set-point on the
temperature controller
Set the thermostat of the temperature controller to
the correct value according to the section “Temperature
control of heating unit”
Defective temperature controller
1) Check the controller: Remove the thermostat
from the valve. If the temperature then increases,
replace the thermostat
2) Alternatively, check and exercise the valve.
Replace the valve if defective
Incorrectly set differential
pressure regulator
Set the differential pressure regulator to the correct value
according to the section “Differential pressure regulator”
Defective differential pressure
regulator
Check and replace if defective
Air bubbles in the system
Bleed the installation thoroughly
Incorrect system pressure
Check the system pressure on a pressure gauge
and top up with water if necessary
The pump is not working
Check whether there is power to the pump
Air in the pump
Make sure there is no air in the pump housing
The pump is blocked
Exercise the pump using the centre screw
The pump has been set at too
low a level
Set the pump correctly, see the section
“Circulation pump UPM3”
Uneven heat distribution in the
building due to incorrectly set
balancing valves on heat emitters
Adjust or install balancing valves
Primary return
temperature
too high
Space heating flow temperature
is too high
Set the thermostat of the temperature controller to the
correct value according to the section “Temperature control
of heating unit”
Defective temperature controller
1) Check the controller: Remove the thermostat
from the valve. If the temperature then increases,
replace the thermostat
2) Alternatively, check and exercise the valve.
Replace the valve if defective
Incorrect setting or dimensioning Check, set, replace
Pump pressure is too high
Set the pump to a lower setting, see the section
“Circulation pump UPM3”
Defective non-return valve
Check and replace if defective
Noise in the unit
Incorrectly set differential
pressure regulator
Set the differential pressure regulator to the correct value
according to the section “Differential pressure regulator”
Defective differential
pressure regulator
Check and replace if defective
Pump pressure is too high
Set the pump to a lower setting, see the section
“Circulation pump UPM3”
