Fault Finding
NB All servicing and repairs must be undertaken by a competent person,
familiar with unvented systems.
Fault
Over temperature cut-out
operates
Regular, intermittent water
discharge from tundish
Continuous water discharge
from the tundish
No water flow from hot taps
Water from hot taps is cold
Possible Cause
The thermostat has failed
The thermostat is set at too
high a temperature
Loss of pressure from the
expansion vessel
Thermostat failure
Pressure reducing valve not
operating correctly
T&P relief valve not operating
correctly
Expansion relief valve not
operating correctly
Cold water mains supply
isolated
Integral line strainer in
pressure reducing valve has
become blocked
Pressure reducing valve
incorrectly fitted
Power supply not switched on
Over temperature cut-out has
operated
Faulty element
Thermostat failure
Solution
Reset. If the cut-out operates
again isolate the unit and
contact the installer.
NB Isolate the electrical
supply before removing the
electrical cover panel and
ensure that the panel is
correctly replaced and
secured before reconnecting
Isolate the heating system and
the mains cold water supply.
Partly drain the unit. Recharge
the expansion vessel to the
specified pressure and
re-commission.
Isolate the heating system and
check thermal controls when
discharge ceases. Replace
thermostat if faulty.
Check with pressure gauge and
replace as necessary
Check and replace if faulty
Check and replace if faulty
Restore mains supply to the
heater
Check and clean as necessary
Refit correctly with arrows in
direction of flow
Check and switch on
See fault "Over temperature
cut-out operates" above
Check and replace as necessary
Check and replace as necessary
AP3/10, AP3/15 Installation Instructions 13
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