Worcester 7735600658, Installation And Maintenance Instructions Manual

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Troubleshooting
25 Greenstar – 6721852556 (2022/11)
Table 27 Domestic Hot Water trouble shooting
Faulty DHW control valve or dirt
inside valve body causing low flow or
no flow though district supply circuit ▶ Check that control valve is functioning correctly,

section 7.3.
▶ Perform re-calibration of control valve,

section 7.2.
▶ Open control valve manually using DHW rotary switch on HIU room controller,

section 7.2.
▶ Clean valve if necessary.
▶ Replace control valve if necessary.
District supply temperature too low ▶ Check that the District supply temperature is correct for the required heat output,

section 13.3 "Domestic Hot Water performance chart".
District flow rate is too low ▶ Check that the District flow rate is correct for the required heat output,

section 13.3 "Domestic Hot Water performance chart".
District supply differential pressure
is too low ▶ Check that the supply differential pressure is correct for the required heat output,

section 13.3 "Domestic Hot Water performance chart".
▶ Adjust any installed flow regulating valves at the heat interface unit to obtain the correct
differential pressure.
▶ Increase the supply differential pressure on the system.
Calcified plate DHW heat exchanger ▶ Check heat exchanger.
▶ Replace heat exchanger.
Cross leaking DHW plate heat
exchanger ▶ Replace heat exchanger.
DHW temperature
too high at the tap HIU control unit incorrectly set or
faulty ▶ Ensure that the DHW temperature set-point is set correctly on the HIU room controller,

section 7.2.
▶ Replace if necessary
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
Electronic keep warm function ▶ 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 control valve is functioning correctly,

section 7.3.
▶ Perform re-calibration of control valve,

section 7.2.
▶ Open control valve manually using DHW rotary switch on HIU control unit,

section
7.2.
▶ Clean valve if necessary.
▶ Replace control valve if necessary.
District supply temperature too low ▶ Check that the District supply temperature is correct for the required heat output,

section 13.3 "Domestic Hot Water performance chart".
District flow rate is too low ▶ Check that the District flow rate is correct for the required heat output,

section 13.3 "Domestic Hot Water performance chart".
District supply differential pressure
is too low ▶ Check that the supply differential pressure is correct for the required heat output,

section 13.3 "Domestic Hot Water performance chart".
▶ Adjust any intalled flow regulating valves at the heat interface unit to obtain the correct
differential pressure.
▶ Increase the supply differential pressure on the system.
DHW over
temperature safety
valve closed DHW control valve stuck in open
position ▶ Check that control valve is functioning correctly,

section 7.3.
▶ Perform re-calibration of control valve,

section 7.2.
▶ Open control valve manually using DHW rotary switch on HIU control unit,

section 7.2.
▶ Replace control valve if necessary.
Faulty DHW over temperature safety
valve ▶ Replace DHW over temperature safety valve.
Cross leaking DHW plate heat
exchanger ▶ Replace DHW plate heat exchanger.
Bypass temperature
higher than 41°C
(+ 5 K) Wrong setting point by room
controller Bypass temperature
higher than 41°C (+ 5 K) ▶ Use the room controller and reset the temperature setting to 41°C (default value) and/
or choose "off" for the bypass function.
Problem Possible cause Possibly solution/check