INSTALLATION AND OPERATION INSTRUCTIONS
2-6
SL 20-115 MODULATING GAS BOILER
until the loop drops ½ the differential below the new load target temperature.
note: if there is no place to sink heat during such Circ. mode, this phase will
continue indefinitely, affecting heat delivery.
thermal shock avoidance is key. Wherever two or more loads are used, and
settings could permit supply temperature differences greater than 20°F, external
3-way motorized or injection mixing is recommended.
a thermal shock avoidance routine is employed to avoid undesirable effects of
large temperature swings: the hot load pump remains on until the boiler’s return
water sensor detects temperature stability - to sink excess heat. For example,
upon satisfaction of a dHW call the dHW load pump will remain running until the
boiler return water temperature falls to the dHW tank target temperature. this
deposits legacy heat from the primary loop into the water tank before activation
of a cooler load.
always ensure that loads sensitive to high temperatures are protected using
appropriate means - e.g. a three way mixing valve set to restrict entering water
temperature to 130°F.
2.5.6 - Error Mode
the controller continually checks sensors to see that they are operating within
normal parameters. if sensors indicate the boiler is operating outside it limits, it
will declare an error condition.
two types of error conditions can occur:
•
Soft Errors:
result when an abnormal condition exists which does not present
an immediate safety hazard. the boiler enters an extended purge, followed
by the error cycle of 5 minutes for all conditions other than Maximum ignition
Trials (a modified Hard Error which locks out for 1 hour after 3 unsuccessful
ignition attempts). Following the purge, the fan and pump are stopped until
the end of the error cycle. normal operation then resumes.
•
Hard Errors:
result when a condition exists that may be a safety hazard.
the boiler enters an extended purge then the fan and pump are stopped.
the boiler is in a lockout, and must be checked and restarted by a service
technician.
With software versions 3.10.0 and higher, the boiler offers an error status signal
feature.
Please see IBC Technical Note: Boiler Status – Analog Output.
See Section 5.3.1 Control Panel
for a list of hard and soft errors and their likely
causes. note that other problems such as disconnected wires or defective
sensors may be the cause of the error. Always check connections and wiring first.
otHer oPerating Features
2.6.1 Prioritization
the control module hosts a scheduling routine to manage the boiler’s operation
when more than one load has been defined. Typically, loads declared as DHW
receive significant - but not absolute - priority. A time vs. differential system will
allocate heat amongst each of up to 3 loads over time.
Multiple heating loads - with varying temperature targets - are run
sequentially
as opposed to
simultaneously
(with a mixing valve). the objective is to serve
each load at the minimum possible temperature, as opposed to running hot
then mixing down – with hardware, saving the related hardware and fuel cost.
The approach optimizes the low temperature combustion benefits of direct cool
2.6
