LAARS HP-M2 Series - Installation, Operation and Maintenance Instructions - Manual (Page 26)

Page 26 LAARS Heating Systems
transfer tank. If no flow check exists or if an existing
flow check is left in the manual (open) position, heat
leaves the bottom of the tank by gravity circulation.
Because of stratification in the tank when the
pump is off, the water around the low limit sensor will
remain hot and the boiler will not replace the heat that
is lost. When domestic hot water is turned on there
will be a short draw of domestic hot water and then,
when the unit pump comes on to start the boiler, the
cold water in the bottom of the tank will be mixed
with the hot water at the top and mix temperature will
be too low to provide adequate domestic hot water and
it will turn cold. If this is the suspected cause feel the
temperature of the piping after the flow check when
the heating system has not been calling for awhile. If
the piping is hot, there is flow past the flow check
which may be causing the problem.
Coil scaling may occur in some areas of the
country where there are high concentrations of
minerals in the water. These minerals may cause
fouling of the domestic hot water coil over an
extended period of time (lime build up) or they may in
rare instances cause a problem in less than a year of
operation. The minerals which react quickly (mostly
magnesium) in well systems cause a slime on the
inside of the coil which prevents adequate heat
transfer. These minerals must be filtered out by a
special incoming water filter or inhibited to protect the
coil and also to provide acceptable water quality. The
minerals contained in public water systems which
accumulate in the coil over long periods of time may
be removed when necessary by flushing the coil with
cleaner such as “Unlime” or “Sizzle”. These products
are also effective in cleaning a coil that is fouled by
magnesium.
12D. High Gas Consumption
(see also Cross Contamination)
Improper burner operation caused by incorrect
air/fuel ratio (CO2 or O2 out of the specified range)
will cause high gas consumption. It is most noticeable
on LP fired units with low CO2 or high O2, however,
units operating on LP or natural gas with incorrect air/
fuel ratios will not provide their best efficiency. If no
combustion analyzing equipment (CO2 or O2) is
available an indication of the air/fuel ratio can be
gotten by briefly sniffing the flue gases. When
running properly the Heat Maker’s flue gases should
have little smell. If they have a strong piercing smell
the gas orifice is probably too small. Do not attempt to
do reorificing without an O2 or CO2 kit.
12E. Shortcycling
(H-M2, HP-M2 Series only)
(see also Cross Contamination)
Possible Causes:
a. No system circulator - low system water flow
b. Small zones - high zone return temperature
The most common causes of short cycling of
H(P)-M2- Series and other low mass boilers is
insufficient hydronic system water flow or small
zones. With H Series this is sometimes caused by the
installer’s failure to install a system circulator as
required in the Installation and Operating Instructions.
The result of low flow is very rapid temperature
rise in the boiler. Sometimes the rise is so fast that the
operating control will not operate before the safety
limit operates. Boiler will reset following cool down
of safety limit thermo element.
Another cause of short cycling is a result of
system design. If one zone in a zoned system has a
very small output, the boiler will only be on for a short
time (when that zone is operating alone) before the
return water comes back to the boiler at a temperature
which will cause the operating control contacts to
open. If this situation causes very rapid cycling it may
be necessary to only operate the small output zone
when another zone is calling. This can be done most
simply (on systems using zone valves) by
disconnecting the end switch wire on the small output
zone one so that the boiler will not be started unless
another zone is calling. This approach eliminates the
need for time consuming repiping. If the on cycles are
at least 1½ minutes long then the short cycling will not
be a problem.
12F. Cross Contamination and
Combustion Related Short Cycling
(units installed with Quick Vent)
Boiler short cycling, nuisance lockouts and
objectionable flue gas odors, may be caused by
leakage of flue products into the combustion air
stream. This results from poorly sealed joints in the
inner (3") pipe. The symptom of this problem is
continual restarts without a lockout occurring. The
“VALVE/FLAME” lite will be on for only a short
time (but more than 6 seconds) before the post purge
starts. This condition is generally seen on new
installations; however, it is possible that a poorly
assembled flue pipe could come apart and cause the
same effect. Cross contamination can best be detected
with a CO2 analyzer (Bacharach® kit for example).
Remove the stack switch tube from the “tee” fitting
above the air orifice and connect the sampling tube of
the analyzer to the "tee". Run boiler and check CO2. If
there is any measurable CO2, cross contamination
exists somewhere in the flue system. If the boiler will
not operate long enough to get a CO2 sample it is
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