LAARS HP-M2 Series - Installation, Operation and Maintenance Instructions - Manual (Page 42)

Page 42 LAARS Heating Systems
15B. Quick Reference Trouble Shooter
FOR MORE INFORMATION SEE INDEX
A. SHORT CYCLING: Unit shuts down before reaching limit. Restarts within one minute without resetting.
1. Cross contamination in air source: remove air elbow from top of air orifice hose coupling and utilize air
from space. (Do not vent both 3" and 5" pipe to chimney)
2. Wrong air or gas orifice combination for size or fuel source. (Refer to gas orifice chart only).
3. Limits operating intermittently or calibration out of specification.
B. UNIT OVERHEATS QUICKLY: boiling noise in combustion chamber.
1. Air in combustion coil or in pump: purge system.
2. Pump failure or control failure.
C. DELAYED IGNITION: Unit starts or stops with a “pop”.
1. Wrong gas orifice for fuel or air orifice size.
2. LP-Gas regulator lock up 3" or greater above run pressure: correct regulator and check gas pipe sizing
against piping chart in installation manual. Set regulator for maximum run pressure of 9" W.C.
3. Remove blower and inspect flame holder (burner) for hole.
4. Check that blower flanges and gas piping are sealed.
D. OCCASIONAL LOCK OUTS: Requires interruption of power to restart.
1. Air in system causes safety limit to open. Vent air from system and determine source of air.
2. Cross contamination in direct vent piping: measure CO² in air supply above air orifice.
(1% or greater will cause lock out and unit damage.)
3. Condensing of moisture in combustion chamber:
a. H-M2 units: No thermostatic union in system supply piping, or thermostat does not
close below 160 °F.
b. HW-M2 units: System circulating pumps not wired to unit “blue” wire.
See field wiring prints in installation manual.
c. Improper pitch of vent pipe allowing moisture to return to combustion chamber or vent
cap installation problem.
4. Occasional failure of blower: red “PURGE” light will be flashing. May also be caused by defective contact
on strap on operating control.
5. Zone control short cycling or voltage problem: Operate thermostats in various sequences to
create suspect problem. Note: TACO zone valves must have isolating relay between end
switch and unit.
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