Honeywell
Heating & Cooling Appliance Controls
Title: Functional description S4965A3025
Doc.: S4965A3025E20
Description Sign. E.C.N. Date Rev.
First issue M.Matiasko 01-Sep-2015 A
Page 15/22
6. Modes of operation
The controller has a number of basic modes of operation:
STAND-BY, when there is no heat demand or error present;
HEAT DEMAND;
ERROR/FAULT conditions like over temperature conditions, sensor faults etc.
The priority of operating modes is fixed as following:
1. Error / Fault mode;
3. Heat Demand;
5. Stand-by mode (Idle).
6.1 - Stand-by
In STAND-BY mode igniter is off and gas valve is off.
6.2 - Heat Demand
When the high or low voltage Heat Demand input is closed, the boiler switch on if no error are present.
The DHW demand is ended when the high or low voltage HD input will be open.
6.3 - Protection and error conditions
Several checks are included to protect the boiler and its environment. Double High Limit sensor is constantly monitored
safety times are constantly compared etc. Any violation of (programmable) limits (and/or internal thermostat functions) will
lead to an error/fault or warning condition. Severe error (igniter lockout) will cause a lockout condition which can only be
cleared by the reset key on the controller itself, or via a closed contact on the reset input. In case of lockout and blocking
conditions, Fan will not operate. Complete list of errors is given as following:
Error codes can be divided in 2 groups:
1. Lockout condition codes;
2. Blocking condition codes.
Error Code Description
LOCKOUT
1 Flame lockout after five ignition trials
2 False flame lockout
3 High Limit error
8 Flame circuit error
9 Gas valve driver circuit error
13 Remote reset lockout
21 ADC error
25 CRC error
40 Lockout on the second Esys
BLOCKING
22 Low Main voltage
26 Internal reset knob blockage
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