4
GENERAL FEATURES
4.1 No Pre-Purge
It is possible to minimise the burner start-up time by bypassing the pre-purge. The major advantage of this control
means that the overall boiler efficiency is increased by minimising the heat loss to the stack during a purge cycle.
This means the burner starts-up quicker therefore reaching setpoint in a reduced time. According to the EN676
European regulation, the burner is allowed to restart without a pre-purge if the burner has recycled due to
operational temperature/pressure. When the burner is stopped by a lockout then this procedure is not allowed,
and the burner will have to start-up as normal with a pre-purge. In order for no pre-purge to be active, valve
proving must take place and finish successfully. If this valve proving operation is successful, then the burner
may start-up without a pre-purge.
In order to initiate the no pre-purge feature, option/ parameter 143 must be set to a value of 1. During the first
start-up the burner will start with a pre-purge initiated. Once the complete commissioning curve has been entered
and the burner has started successfully, the burner will then start-up every time with no pre-purge. If the burner
goes above its setpoint and turns off on high temperature/ pressure, then the next time the burner starts-up, it
will go through the VPS operation and then light off without a pre-purge, i.e. the burner has shut down in a
controlled manner and the gas valves have been checked for integrity.
According to the EN676 regulation, the burner is only allowed to work in this manner if VPS operation has been
set to operate before the burner starts up; option/parameter 129 must be set to 0.
The start sequence without pre-purge is as follows:
1.
Firstly, the system goes through its internal tests and relay checks.
2.
Call for heat on Terminal 57 activates and the system will go through the VPS operation.
3.
If this operation is successful, then the MM will drive the channels to the light off or start position.
4.
Once all channels reach the start position then the burner will light off.
If the burner shuts down in an abrupt manner, e.g. loss of power to the unit, then the next time the burner starts-
up a complete purge will be initiated.
If no pre-purge is enabled in option/parameter 143, and one or more of the following conditions occur, the
next time the burner starts up, a complete pre-purge will be initiated:
• Burner lockout
• Loss of power to the MM
• VPS checks have failed
• MM has been in standby for 24 hours or more
Note: Pre-purge is only available on fuels which are optioned as gaseous.
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