QUICK REFERENCE
5.2 NORMAL OPERATION
The C45, C40P and C55(P) boilers feature a user display which shows actual flow temperature at
all times (the last two digits of the display) and a status number (the first digit) which identifies
what the boiler is doing at any given time. The table below shows the range of status codes which
will be displayed as part of normal boiler operation:
NORMAL OPERATION CODES
Temporary mode whilst boiler is adjusting internal settingsA nn
Boiler pump is in DHW overrun mode (2 mins)8 nn
Boiler pump is in Central Heating overrun mode (2 mins)7 nn
Burner is off because the boiler is up to temperature6 nn
Temporary mode whilst boiler is adjusting internal settings5 nn
Boiler is alight and running in response to a demand from DHW (i.e. SL2)4 nn
Boiler is alight and running in response to a demand from central heating (i.e. SL1)3 nn
Boiler has opened gas valve and is sparking at ignitor2 nn
Boiler is running fan prior to attempting ignition1 nn
Boiler in standby waiting for demand signal0 nn
MeaningDisplay
5.3 FAULT MODES
5.3.1 Automatic Lockout Avoidance
The boiler will react to adverse conditions in two ways. If the fault is not severe, or is not
persistent, the boiler will halt (or block) operation for a set time before it attempts to fire again.
During this block time the block code will be displayed, alternately with the code “9 nn”, where nn
is the boiler flow temperature.
BLOCK CODES
Waiting for fan to startB 65
Difference between flow and return temperatures too high. Check water circulationB 30
Incorrect signal from fan. Possible fan faulty.B 29
No signal from fan. Possible fan disconnected or faulty.B 28
Low water pressureB 26
Flow temperature climbing too quickly. Possible air lock or circulation blockageB 25
Return temperature exceeded flow temperature. Check pump direction on boiler
and any external pumps. Check wires on flow and return thermistors are not
crossed.
B 24
Return temperature exceeded 95
o
CB 19
Flow temperature exceed 95
o
CB 18
Reason for blockDisplay
WD536 Chapter 5 : Fault Finding The Keston C45, C40P, C55 & C55P
Installation & Servicing Instructions Page : 29
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