Specifications

56 – Service VMBMH302
15.4.4 Hot water
Problem – Temperature and/or quantity
Cause Troubleshooting Remedy
1. Defective 3-way valve motor. Check the function of the 3-way valve,
that it runs between the end positions by
running a manual test.
If the motor is defective, replace it.
2. Jammed 3-way valve insert.
The valve is not secure and relea-
ses hot water to the radiators
during hot water production.
Detach the motor and test closing and
opening of the valve by pressing the
control arm
If the insert jams, remove and clean it, or
replace it.
3. Air in TWS coil or water outer
jacket.
During hot water production:
• Listen for air.
• Check the temperature difference bet-
ween supply and return line.
Bleed the system.
A Large temperature difference can indi-
cate air in the system.
4. Start temperature set too high
for hot water production.
Check that the start temperature is cor-
rectly set. Should not be set above the
factory set value.
• 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.
5. Sensor fault, hot water sensor.
Hot water production is started
by the hot water sensor.
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 section
15.3 Measurement points.
If the sensor is defective, replace it.
6. Large drain flow (>12l/min). 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.
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.
7. Water heater too small in rela-
tion to requirement.
How large is the requirement and what is
the capacity of the heater?
Replace with a larger heater or supple-
ment with an extra heater.
E.G. supplement with an DWH TWS or an
electric heater.
8. The operating pressure switch
opens too soon (at too low a
pressure).
Hot water production ends when
the operating pressure switch
opens.
Check the break pressure using manome-
ter apparatus.
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)
9. Insufficient exchange surface
to transfer the heat pump’s out-
put to the heater.
(Only applies to heat pumps with
a separate heater)
Is the exchange surface too small?
Can the heater cope with the heat
pump’s output?
Replace with a heater with a larger
exchange surface.