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March 2011
Flex Fuel Owner’s Manual
13: Pellets Auto Control
Pellets mode!
The furnace regulates in “Pellets mode!” as long as there is a call for heat and the furnace temperature is
lower than the set “boiler target temperature“. The speed of the induced draft fan and the pellets fill
level in the firebox will vary depending on the measured furnace temperature, flue gas temperature and
air factor. Once the call for heat has been met, the furnace switches off and outputs the
message “No request! Fan lag!”.
No request! Fan lag!
All calls for heat has been met; the furnace completes “Pellets mode!” by initiating “Fan lag!”. Fan
lag ends when the flue gas temperature falls below the factory default switch-off threshold and the
preset run-on time has elapsed. The furnace then switches to standby mode (“Availability!”) and
automatically restarts when there is a call for heat.
Required boiler temperature is reached! Fan lag!
The set furnace target temperature has been reached. The furnace completes “Pellets mode!” by
initiating “Fan lag!”. Fan lag ends when the flue gas temperature falls below a preset threshold and the
subsequent run-on time has elapsed. The furnace then switches to standby mode (“Availability!”) and
automatically restarts when there is a call for heat.
Boiler is switched off! Fan lag!
The furnace was switched off in operational state “Ignition phase”, “Start phase!” or “Pellets mode!”. The
furnace completes pellets operation by initiating “Fan lag!”. Fan lag ends when the flue gas temperature
falls below the switch-off threshold and the run-on time has elapsed. The furnace then switches to
operational status “Boiler is switched off!“. Only when the operational status “Boiler is switched off!” has
been reached is it possible to switch the furnace back on in operating mode “Pellets auto control”.
Heat exchanger cleaning required! Fan lag!
The furnace will quit pellets mode to perform the heat exchanger cleaning. Fan lag ends when the flue
gas temperature falls below the switch-off threshold and the run-on time has elapsed. The furnace then
automatically cleans its heat exchanger and automatically restarts if a heating circuit demand is present.
Heat exchanger cleaner waiting to be released!
The furnace requires heat exchanger cleaning, before it can start but is still waiting for a release.
Heat exchanger cleaning is released if:
• a time release is set
• the furnace has cooled
• the flue gas temperature is below the factory default release point
Heat exchanger cleaning is active!
The furnace is carrying out its heat exchanger cleaning. The duration of the cleaning impulse is system
specific and can vary between 3 and 20 minutes. After the end of cleaning, the furnace starts
automatically once a heating circuit demand exists.
