andrews R18 Series, Technical Documentation Manual

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18IP22B
45
7.8 Fault finding table
Fault Possible cause Solution
Water heater does not No electrical supply to Check whether switched
attempt to light water heater indicator (1) is alight
No heat demand Check control thermostat
High limit thermostat has If lamp 2 is illuminated,
operated press reset button and
End switch gas valve is Check end switch gas
not in rest position valve
Insufficient water flow check water system
indicator (5) alight
Control panel fuse blown Check fuse
Faulty control box Change box
Check all external con-
trols for continuity
is set high enough
allow unit to fire. If lamp
4 then illuminates, reset
button in high limit ther-
mostat (see 7.4)
Check air damper relais,
replace if necessary
Air damper cycles and Micro switch minimum Readjust minimum set-
water heater does not
light setting (
II
) servo motor is ting micro switch (
II
)
set above 20 % servo motor
Heat demand Closed control switch Check and repair
Servo motor does not main gas valve is inope-
react rative
Turn open relay inopera- Replace turn open relay
tive
Up signal is present at Check servo motor con-
contact 22 nector, if operative re-
place servo motor
Heat demand Micro switch maximum Readjust maximum set-
Servo motor turns the air
damper only open but
not close
setting ( I ) is not set cor- ting micro switch ( I )
rectly
Micro switch contact is Replace servo motor
coroded or broken,
no voltage at contact 23
There is voltage at con- Replace close down re-
tact 23 but close down lay
relay does not react
Heat demand No voltage at contact 21 Check 20 % setting mi-
Servo motor opens en cro switch, readjust.
closes the air damper but If this does not correct
water heater does not problem replace servo
start motor
Voltage at contact 21 If relay does not react
and 20 % micro switch is replace requisite relay
operative. Check pre re-
quisite relay