Bosch SSB1000 TL - Low Water Cut-Off Function

SSB 6720892984 (2019/02) US
Main control | 39
Relevant variables
Specic Parameters Level (Default) Value Range
De_Air_Cong
0 = DAir disabled;
1 = DAir enabled.
2: Installer 0 0..1
De_Air_State
Current state of the DAir
function.
1: User - -
DAir_Repeation_
OnOff
Number of repeating ON/
OFF.
2: Installer
2 0..255
DAir_Number_Cycles
Number of DAir cycles..
2: Installer 10 0..255
5.3.15 Low water cut off (Rev 3.0.0.0)
A Low Water Cut Off (LWCO) sensor can be enabled to detect if there
is enough water in the boiler. When this is not the case a non-volatile
lockout error is generated.
Relevant variables
Specic Parameters Level (Default)Value Range
Programmable input
LWCO 1
3: Factory 0
0 ¨ Disabled
1 ¨ Enabled
Programmable input
LWCO 2
3: Factory 0
0 ¨ Disabled
1 ¨ Enabled
5.3.16 Heat exchanger protection (Rev 3.0.0.0)
Heat Exchanger Protection limits the max. heat load based on the heat
exchanger ow (CH ow).
To avoid temperature differences that are too large in the primary heat
exchanger, the burner load automatically decreases when the CH water
ow decreases too much.
• Above
Nominal_EX_Flow_Rate the maximum burner power is
available.
• At
Min_EX_Flow_Rate the minimum burner power is available.
• Below
Min_EX_Flow_Rate the burner is stopped.
In between
Nominal_EX_Flow_Rate and Min_EX_Flow_Rate , the
burner power is linear limited.
To achieve this the PID output value is linear limited between
Nominal_
EX_Flow_Rate
and Min_EX_Flow_Rate .
However, when the calculated PID output for temperature control is
already below this limit, this output value remains the current control
value. The power limitation will be performed only in Burn status.
Consequentially in Pre-Purge status the fan power is always @ 50% of
maximum power available.
When a demand request is present the level of the ow is evaluated. If
the ow is too low (smaller than the
Min_EX_Flow_Rate parameter)
and stays low for at least (
PRE_PURGE_TIME - 2 seconds), a warning
is raised (
LOWEXFLOW_PROTECTION warning). Although the timeout is
limited between a minimum value of 4 seconds and a maximum value of
60 seconds.
In case the ow level is too low the fan will be switched OFF in order to
protect the heat exchanger while the pump stays On. When the level of
the ow will be again stable for at least 20 seconds the warning status
is cleared and the burner will go again in BURN status if a request is still
pending. In case the request of demand has been cancelled the burner
will go in STANDBY.
Max. available power (%)
Min. Flow Nominal Flow
M
ax. (100%)
Min
Flow (m
3
/h
)
0%
Based on the value of the Nominal_Flow parameter there are two
case of low ow protection behaviour.