Domestic Hot Water Trouble Shooting Guide - Bosch Worcester Greenstar HIU E Installation And Maintenance Instructions Manual

Fault finding and diagnostics
Problem Possible cause
Central heating flow HiU Control unit incorrectly set or
temperature too faulty
high
Room controller incorrectly set or
faulty
Central heating flow sensor out of
position or faulty
Faulty central heating control valve
or dirt inside valve body causing
valve to seize.
Table 32 Central heating trouble shooting
9.2

Domestic hot water trouble shooting guide

Problem Possible cause
Hot water flow rate Domestic cold water inlet filter
is too low or no flow blocked
Inlet water pressure too low
DHW safety valve has closed due to
a seized DHW control valve
DHW temperature HIU Control unit incorrectly set or
too low or varies faulty
excessively at the
tap
DHW flow turbine faulty
Faulty DHW control valve or dirt
inside valve body causing low flow
or no flow through district supply
circuit
District supply temperature too low ▶ Check that the district supply temperature is correct for the require heat output. 
District flow rate is too low
District supply differential pressure
is too low
Calcified plate DHW heat
exchanger
Cross leaking DHW plate heat
exchanger
DHW temperature HIU Control unit incorrectly set or
too high at the tap faulty
Table 33 Domestic hot water trouble shooting
60
Possibly solution/check
▶ Adjust HIU control unit. Ensure that the flow temperature set-point is set correctly on
the HIU controller.  section 6.4
▶ Replace if necessary
▶ Adjust room controller. Ensure that the flow temperature set-point is set correctly on
the HIU controller.  section 6.4
▶ Replace if necessary
▶ Ensure sensor is in correct position.
▶ Replace sensor
▶ Check that control valve is functioning correctly.  section 6.5
▶ Perform re-calibration of control valve.  section 6.4
▶ Open control valve manually using CH rotary switch on HIU control unit.  section 6.4
▶ Replace control valve if necessary
Possibly solution/check
▶ Ensure minimum inlet water pressure is 1.5-2 bar.
▶ Clean filter
▶ Increase domestic cold water supply pressure into HIU by consulting the water supply
company.
▶ Clean plate heat exchanger if there are signs of calcification.
▶ 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
▶ Clean valve if necessary.
▶ Replace control valve if necessary.
▶ Ensure that the DHW temperature set-point is set correctly on the HIU controller.
 section 6.4
▶ Replace control unit if necessary.
▶ Check electrical connections to flow turbine.Replace if necessary.
▶ 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
▶ Clean valve if necessary.
▶ Replace control valve if necessary.
figure 55, Domestic hot water performance chart
▶ Check that the district flow rate is correct for the require heat output.  figure 55,
Domestic hot water performance chart
▶ Check that the supply 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.
▶ Check heat exchanger.
▶ Replace heat exchanger.
▶ Replace heat exchanger.
▶ Ensure that the DHW temperature set-point is set correctly on the HIU controller.
 section 6.4
▶ Replace if necessary
6 720 808 928 (2017/06)