Fault finding and diagnostics
6 720 808 928 (2017/06) 61
9.3 HIU Control unit LED indications
Time taken to get
hot water at the tap
is too long
Mechanical by-pass valve has dirt
inside valve body
▶ Clean valve if necessary.
Mechanical by-pass valve is set
incorrectly, or is faulty
▶ Adjust by-pass valve.
▶ Replace if necessary.
Faulty DHW control valve or dirt
inside valve body causing low flow
or no flow though district supply
circuit
▶ Check that the control valve is functioning correctly. section 6.5
▶ Perform re-calibration of control valve. section 6.4
▶ Open control valve manually using DHW rotary switch on HIU control unit.
section 6.4
▶ Replace control valve if necessary.
District supply temperature too low
▶ Check that the supply temperature is correct for the required heat output.
figure 55, Domestic hot water performance chart
District flow rate too low
▶ Check that the flow rate is correct for the required heat output.
figure 55, Domestic hot water performance chart
District differential pressure is too
low
▶ Check that the differential pressure is correct for the required heat output.
figure 55, Domestic hot water performance chart
▶ Adjust the flow regulating valves at the Heat Interface Unit to obtain the correct
differential pressure.
▶ Increase the supply differential pressure on the system.
Domestic hot water circulation
pump out of operation
▶ Check that the pump is running correctly and that there is no air in the pump.
DHW safety valve
closed
DHW control valve stuck in open
position
▶ Check that control valve is functioning correctly. section 6.5
▶ Perform re-calibration of control valve. section 6.4
▶ Open control valve manually using DHW rotary switch on HIU control unit.
section 6.4
▶ Replace control valve if necessary.
Faulty DHW safety valve ▶ Replace DHW safety valve.
Cross leaking DHW plate heat
exchanger
▶ Replace DHW plate heat exchanger.
Reason or Error
Left LED
(DHW)
Right LED
(CH) Outcome
Outdoor temperature sensor error No No No set point is set in case of weather compensated control
- CH function does not detect a heat demand
CH flow temperature sensor error - Red CH and frost protection functions are disabled
CH return temperature sensor error - Yellow Limit return temperature functions are disabled
DHW volume flow sensor error Red - DHW and circulation pump functions are disabled
DHW flow temperature sensor error Red - DHW and circulation pump functions are disabled
Supply flow temperature sensor error Red - By-pass, DHW and circulation pump functions are disabled
Supply return temperature sensor error - Yellow Limit return temperature function is not working
Supply flow temperature lower than CH or DHW set
points
Yellow Yellow Just error detected, HIU will keep on trying to supply heat
Supply flow temperature higher than allowed (95 °C) Red Red Control valves will be kept closed and so no function
except CH pump running can be executed
If a net connected HIU detects a CH module, a low loss
header must be installed and its temperature sent to the
HIU. If this temperature is not available the error
becomes true
- Red CH function is disabled
PWM feedback signal indicates a CH control valve error - Red CH and frost protection functions are disabled
PWM feedback signal indicates a DHW control valve error Red - By-pass, DHW and circulation pump functions are disabled
CH rotary switch position is invalid - Red flashing CH function is disabled
DHW rotary switch position is invalid Red flashing - By-pass, DHW and circulation pump functions are disabled
Table 34
Problem Possible cause Possibly solution/check
Table 33 Domestic hot water trouble shooting
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