LAARS Rheos+ RHHV - Install and Operating Manual - Manual (Page 45)

LAARS Heating Systems Page 44
6. When the call for heat is complete, or the unit
reaches its setpoint temperature, the gas valve
will close, and the fan will continue to run for
its 30 second post-purge. If a pump time delay
is used, the pump will continue to run for the
specified amount of time (adjustable from 0.1 to
10 minutes).
8.2 Resolving Lockouts
There are many causes of lockouts. The four
most common causes are: (1) inadequate gas supply,
(2) poor combustion, (3) ignitor failure (4) combustion
air.
1. Inadequate gas supply: Before proceeding, ensure
that the gas supply has not been shutoff or the LP
tank (LP boilers) is not empty. Then, restart the
boiler and observe the operational cycle. After
the pre-purge time, the unit should light. If it
does not, consult the factory.
2. Poor Combustion: Poor combustion should be
suspected if there is a strong flue gas odor. The
odor may result from an improper gas/air ratio
(high or low O
2
or CO
2
). If an improper gas/air
ratio is suspected, consult the factory.
3. Ignitor failure: If the boiler goes through a
normal start cycle but combustion does not
occur, ignitor failure should be suspected. Check
the ignitor by unplugging the ignitor plug and
measuring the ignitor resistance. It should be
50-80 (Ω) ohms. If the resistance is not 50-80
ohms (Ω), replace the ignitor. If the resistance is
correct, reset the boiler and check for 120 VAC
at the ignitor plug during the start cycle. If there
is no voltage, replace the faulty ignitor wire
harness.
4. Inadequate combustion air: If the boiler goes
through a normal ignition cycle, and shuts off
after the blower ramps up to full speed, an
abnormal restriction in the air intake or exhaust
system should be suspected. Check the air filter
for buildup of debris and clean filter if necessary.
Inspect all exhaust venting and intake venting for
blockages. Remove any blockages and inspect
and replace any damaged vent sections. If the
unit still continues to lockout after igniting,
consult the factory.
Once the reason for the lockout has been
identified and resolved you can reset the unit by
pressing the manual reset button (see Detail A in
Figure 30, Control Panel).
8.3 Delayed Ignition - Possible Causes
8.3.1 High Lockup Pressure (LP
Appliances) - Occurs on Start-up
High lock up pressure is the most common
cause of delayed ignitions on LP fueled appliances. It
may result from an improper second stage regulator
selection or from a faulty regulator.
Lock up can be detected by measuring the gas
supply pressure to the appliance at the inlet pressure
port on the gas valve. The gas supply to the appliance
must be shut off before making any connections. To
check: use a water manometer or pressure gauge with
a scale reading of at least 25 in. W.C. or 15 oz/in 2 .
(6.2kPa). Attach the manometer to the gas valve inlet
pressure port. Turn on the gas supply. The Rheos+
appliance is designed to operate with supply pressures
of 4-13 in. W.C. (2.3 - 7.5 oz/ in²) (1.0-3.2kPa). If
the supply pressure exceeds 13 in. W.C. (7.5 oz/ in²)
(3.2kPa) (with the appliance off) it is possible that this
may be the cause of the delayed ignitions and the inlet
pressure must be reset to between 4-13 in. W.C. (2.3
– 7.5 oz/in 2 ) (0.1-3.2kPa). Restart the appliance and
then switch it off. If the inlet gas pressure exceeds 13
in. W.C. (7.5 oz/ in²) (3.2kPa) after the appliance is
switched off, correct the lock up problem.
8.3.2 Gas Valve Regulation
Gas valve regulation problems can also cause
delayed ignitions. If gas valve regulation problems
are suspected, consult the factory. Do not attempt field
adjustment or repair.
8.3.3 Defective Burner - Occurs on
Startup or at Burner Shutdown
A defective burner can cause a delayed ignition.
If the gas supply pressure is proper, and the gas valve
is functioning properly, the burner should be inspected.
There should be no distortion or perforations in the
burner. Replace if indicated.
8.4 Short Cycling — Boiler
Because the Rheos+ is a modulating boiler, and
its input will decrease when there is a reduction in
heating load, short cycling is greatly reduced. If the
heating load drops below the minimum input of the
boiler for an extended period, the boiler will have
a tendency to short cycle. This can be a symptom
of improper control strategy or setpoints, or a load
distribution problem. See Section 5.5 regarding
controller setup. Contact your LAARS representative
to discuss possible remedies.