Danfoss DHP-A Service Instructions Manual page 20

Service instructions
2.4.4 Hot-water
Problem – Temperature and/or quantity
Cause
1. Defective 3-way valve motor.
2. Jammed 3-way valve insert.
The valve is not secure and releases
hot water to the radiators during
hot water production.
3. Air in TWS coil or water outer
jacket.
4. Start temperature set too high for
hot water production.
5. Sensor fault, hot water sensor.
Hot water production is started by
the hot water sensor.
6. Large drain flow (>12l/min).
7. Water heater too small in relation
to requirement.
8. The operating pressure switch
opens too soon (at too low a pres-
sure).
Hot water production ends when
the operating pressure switch
opens.
20
Domestic heat pumps
Troubleshooting
Check the function of the 3-way valve, that it runs
between the end positions by running a manual
test.
Detach the motor and test closing and opening of
the valve by pressing the control arm
During hot water production:
▪ Listen for air.
▪ Check the temperature difference between
supply and return line.
Check that the start temperature is correctly set.
Should not be set above the factory set value.
Check what the hot water sensor (the start sensor)
shows. Is it a plausible/actual value?
Measure the resistance of the sensor, check against
the ohm table, see chapter Measurement points.
Check how many litres of hot water (approximately
40°C) per minute drains from the tap. Use a clock
and bucket to measure the drain flow.
How large is the requirement and what is the ca-
pacity of the heater?
Check the break pressure using manometer appa-
ratus.
VIGFI102
Remedy
If the motor is defective, replace it.
If the insert jams, remove and clean it, or re-
place it.
Bleed the system.
A Large temperature difference can indi-
cate air in the system.
▪ If the start value is set too high, reduce
it to the factory set value.
▪ If the system has a high (>+8°C) brine
temperature, you may have to reduce
the start value further for a longer run-
ning time.
If the sensor is defective, replace it.
If the drain water flow is greater than 12l/
min, stratification in the water heater is af-
fected, which reduces the hot water capaci-
ty.
Suggested corrective actions:
▪ Install a pressure reduction valve on
the incoming cold water pipe.
▪ Change to a mixer with lower flow.
▪ Adjust the drain flow on the existing
mixer, do not open the tap fully.
Replace with a larger heater or supplement
with an extra heater.
E.g. supplement with an DWH or an electric
heater.
If the pressure switch opens at the incorrect
pressure, replace it.
The replacement pressure switch can be in-
stalled on the service output (Schrader
valve).
Danfoss Heating Solutions