Danfoss DHP-A Service Instructions Manual page 51

10.4.4 Hot-water
Table 29. 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 pressure).
Hot water production ends when the
operating pressure switch opens.
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 con-
trol arm
During hot water production:
•
Listen for air.
•
Check the temperature difference
between supply and return line.
Check that the start temperature is cor-
rectly 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 in Measure-
ment points.
Check how many litres of hot water
(approx. 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 capacity of the heater?
Check the break pressure using manome-
ter apparatus.
Remedy
If the motor is defective, replace it.
If the insert jams, remove and clean it, or
replace 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 running time.
If the sensor is defective, replace it.
If the drain water flow is greater than
12l/min, stratification in the water
heater is affected, which reduces the hot
water capacity.
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 exist-
ing mixer, do not open the tap fully.
Replace with a larger heater or supple-
ment with an extra heater.
E.g. supplement with an DWH or an
electric heater.
If the pressure switch opens at the incor-
rect pressure, replace it.
The replacement pressure switch can be
installed on the service output (Schrader
valve).
Service instructions VMGFC302 – 49