6 MM Features
Mk8 MM Manual Page | 136
6.11 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.
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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