P-K MACH
®
Gas Fired Boiler
Technical Service 1.877.728.5351
Revised: January 3, 2020
Released: January 3, 2020
Patterson-Kelley 2020
All Rights Reserved.
1004905981 P-K MACH C1500H-C4000 Installation and
Owners Manual (Rev F Jan-2020).docx
Page 67
Sequence of Operations
1. When the Boiler On/Off switch is turned on, power is provided
through over-current protection (fuse and/or circuit breaker) to
the boiler control and the combustion blower.
2.
When the outlet water temperature drops below “
CH
SETPOINT
” minus “
CH DIFFERENTIAL ON
”, a heat request is
generated.
3. Provided all limits are made and the remote enable signal (if
installed) is active, the boiler will attempt to start.
4. The NURO control checks to make sure air pressure switch is
open indicating there is no airflow through the boiler. The
combustion blower is then driven towards the pre-start fan
speed.
When the air pressure switch closes, the “
PRE PURGE
TIME
” timer is started. Once the “
PRE PURGE TIME
” timer
expires, the blower is driven to the ignition speed.
5. A trial for ignition begins and the sequence of events is
illustrated graphically below. A valid flame signal must be
detected within 4 seconds after the gas valves open (elapsed
time 7 seconds).
6. After a successful ignition, the fan is driven to low fire and the
“
CH LOW FIRE HOLD TIME
” timer is started. Once the “LOW
FIRE HOLD TIME” timer expires, the boiler is released to
modulation.
7. The NURO Control modulates the firing rate between low and high fire to maintain the desired
outlet water temperature.
8.
The burner will continue firing until the outlet water temperature exceeds “
CH SETPOINT
” plus
“
CH DIFFERENTIAL OFF
”. At this temperature, the gas valves are closed combustion air fan
continues to run until the “
POST PURGE TIME
” timer has expired.
9. When the outlet water temperature is reduced by the load on the system, a heat request is
generated. The operating sequence will recycle to
Step 3
.
If any
“Manual Reset” limit
device trips, DO NOT reset
without determining and
correcting the cause. Manual
Reset Limits include: Flame
safeguard, high or low gas
pressure, high temperature
limit, stack temperature, low
water level. Attempting to
operate a boiler without
diagnosing the cause of failure
can result in unsafe operation,
increasing the risk of injury.
Never attempt to bypass a
safety limit device.
N
OTICE
!
Once the boiler begins the
ignition sequence, the firing
sequence will continue until
main flame is reached
regardless of heat request.
The sequence can be
interrupted by turning the
power switch off.
