36
Stack limit exceeded displayed on screen
Alert 125: Modulation was limited due to stack limit
Alert 353: Abnormal recycle: stack limit
A flue gas error occurs when the stack temperature has exceeded the maximum limit allowed by the vent material. This is an
automatic reset error, when the stack temperature drops 20
o
F below the limit allowed the boiler is allowed to restart and an ignition
attempt is made if the call for heat is not yet satisfied. In the event that a setpoint greater than 150
o
F is selected and PVC venting is
used the setpoint must be reduced to below 150
o
F to avoid nuisance flame failures. If a setpoint greater than 150
o
F is required,
venting with CPVC, AL29-4C, 316LL or PPE is strongly advised.
The stack temperature is between 15-30
o
F above the incoming (return) water temperature to the appliance.
Vent Material
Maximum Flue Temperature [
o
F]
PVC
149
CPVC
194
PPE
230
AL29-4C
300+, limited only by rating of seals
316L Stainless Steel
300+, limited only by rating of seals
Is vent material PVC plastic?
(white in colour)
YES
Adjust CH and/or
DHW Setpoint to
150
o
F or less to avoid
nuisance trips
NO
Select the correct vent
material setting through
boiler display
