H E A T I N T E R F A C E U N I T
T R O U B L E S H O O T I N G
Page 30
H E A T I N T E R F A C E U N I T
T R O U B L E S H O O T I N G
Page 31
10. TROUBLESHOOTING
FAULT
POSSIBLE CAUSE
REMEDY
No Water From DHW
Outlets
1. Mains cold water supply lost / shut off
Check cold water supply to HIU / MCW
outlet / contact local water authority if
necessary
2. Cold water check valve installed in
incorrect direction
Check direction of flow arrows on the valve.
Refit correctly if necessary
3. DHW or MCW isolation valves on HIU
are closed
Open mains cold water and/or domestic hot
water valves on HIU, determine reason for
isolation first to ensure secondary systems
are complete
4. MCW strainer is blocked
Remove and clean MCW strainer
Reduced Flow Rate From
Outlets
1. Low mains water pressure
Check pressure, consult local water authority
if necessary
2. Plate heat exchanger is partially blocked
Remove PHE, clean and re-install or replace
if necessary
3. Size of service pipe to HIU is too small
Pipe size should be increased
4. DHW or MCW isolation valves on HIU are
partially closed
Open DCW and/or DHW valves on HIU
5. MCW strainer is blocked
Remove and clean MCW strainer
1. Check if HIU has power supply
Determine whether HIU is safe, if
determined safe turn power supply on. If HIU
fused outlet is on check local fuse, if fuse is
operating correctly check circuit breakers
No Hot Water
2. HIU primary isolation valves closed
Open primary flow and return isolation
valves
3. DHW temperature in actuator is not set
correctly
Check setting of actuator and re-adjust if
necessary
4. DHW PICV / Actuator is not operating or
set correctly
Check setting of PICV, check operation of
actuator and replace if necessary
5. Primary prepayment valve is closed (if
installed)
Check if valve open, check power supply to
actuator, if power present replace actuator
with correct model
6. Local TMV faulty
Check TMV for correct operation, blockages
or setpoint / to confirm TMV issue check
DHW outlet temperature from outlet
without thermostatic mixing
7. No or low flow from primary system
Check flow rate on heat meter and consult
network operator if necessary
8. HIU primary strainer is blocked
Isolate HIU electrically and mechanically,
allow to cool, remove and clean strainer(s)
9. Low flow temperature from primary
system
Check flow and return temperature on heat
meter to confirm connected correctly, if
connected correctly and flow temperature is
low consult network operator
10. Plate heat exchanger is blocked
Remove PHE, clean and re-install or replace
if necessary
FAULT
POSSIBLE CAUSE
REMEDY
No Heating
1. Check if the HIU has power supply
Determine whether HIU is safe, if
determined safe turn power supply on. If
HIU fused outlet is on check local fuse, if fuse
is operating correctly check circuit breakers
2. Room stat or programmer is incorrectly
set or faulty
Check HTG control operation, replace if
necessary
3. Primary / secondary isolation valves on
HIU are closed
Check valves and open if necessary
4. HTG temperature in actuator is not set
correctly
Check setting of actuator and re-adjust if
necessary
5. HTG PICV / Actuator is not operating
Check operation of actuator and replace if
necessary
6. Primary HTG On/Off valve is closed
Check if valve open, check power supply to
actuator, if power present replace actuator
with correct model
7. Primary prepayment valve is closed (if
installed)
Check if valve open, check power supply to
actuator, if power present replace actuator
with correct model
8. Low secondary heating system pressure
Connect filling loop and introduce pressure,
vent radiators, remove filling loop when
complete
9. Air lock within HTG system
Vent all radiators and top up system
pressure as required
10. HTG circulation pump not working or set
incorrectly
Check HTG pump for correct setting and
operation, replace if necessary
11. High temperature cut-off switch set too
low / is faulty (if installed)
Check setting against design parameters
and operation of cut-off switch / replace if
necessary
12. No or low flow from primary system
Check flow rate on heat meter and consult
network operator if necessary
13. Primary or secondary strainers are
blocked
Isolate HIU electrically and mechanically,
allow to cool, remove and clean strainer(s)
14. Low flow temperature from primary
system
Check flow and return temperature on heat
meter to confirm connected correctly, if
connected correctly and flow temperature is
low consult network operator
15. Plate heat exchanger is blocked
Check HTG pump for correct operation,
replace if necessary
Water Discharging From
Safety Valve
1. Pressure above 3 bar
Shut down HIU, check charge of expansion
vessel and ensure filling loop is closed
2. Faulty Safety Valve
Test pressure in space heating if below 3 bar,
replace safety valve if necessary
Pressure Fluctuating
Within Heating System
1. Faulty expansion vessel
Check charge (1 bar) within expansion vessel,
re-charge or replace if necessary
