Danfoss DHP-AL Installation And Service Instructions Manual page 51

Cause
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 oper-
ating pressure switch opens.
9. Insufficient exchange surface to transfer
the heat pump's output to the heater.
(Only applies to heat pumps with a separate
heater)
10. Heat loss in the hot water pipe.
Troubleshooting
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 in the "Measurement
points" section.
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 manometer
apparatus.
Is the exchange surface too small?
Can the heater cope with the heat pump's
output?
Open the hot water tap, read off the tem-
perature on the outgoing hot water pipe
from the heat pump and the temperature of
the hot water. The temperature difference
measured between the heat pump and hot
water indicates the temperature loss.
Examples of temperature loss causes:
• Long water pipes.
• Uninsulated hot water pipes.
• Hot water pipes routed through cold areas.
Other causes that can affect the hot water
temperature:
• Is a mixer valve installed in the system?
Temperature set too low on the mixer
valve? Leaking mixer valve?
• Water tap fault? Leaking thermostat mixer?
VMBME102
Remedy
• If the start value is set too high, reduce it
to the factory set value.
• If the system has a high (>+8°C) brine tem-
perature, 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 existing mixer,
do not open the tap fully.
Replace with a larger heater or supplement
with an extra heater.
E.G. supplement with an MBH TWS +
Connector or an electric heater.
If the pressure switch opens at the incorrect
pressure, replace it.
The replacement pressure switch can be
installed on the service output (Schrader
valve)
Replace with a heater with a larger
exchange surface.
If any problems occur during troubleshoot-
ing as per the points, carry out corrective
actions.
To quickly check that the heat pump's hot
water production works as it should, drain
the hot water so that the heat pump starts
to produce the hot water. When done, read
off the temperature on the top sensor and
on the start sensor. The top sensor should
show a temperature of around 50-55°C and
the start sensor around 45-48°C. If, after
completed hot water production, these
temperatures are obtained, this means that
you have the correct temperature and vol-
ume of hot water in the water heater.
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