LAARS NeoTherm NTV (Sizes 150–285 MBTU/h) - Service Manual - Manual (Page 63)

53 Service Manual NeoTherm 80 - NeoTherm 285
Possible Combustion Problems
About Correct Combustion
When the unit is firing, the gas valve must always supply the correct amount of gas to
match the amount of air going through the burner. The ratio of gas to air remains con-
stant, but the control module adjusts the blower speed to adjust for changes in heat load.
If the ratio of gas to air is not correct, this will cause poor combustion, and this can cause
several different problems:
• Poor combustion can cause the unit to produce carbon monoxide, and this may lead
to personal injury or death.
• Poor combustion will make the unit run less efficiently, and cause it to use more gas
than necessary.
• Poor combustion can cause maintenance problems, including sooty exhaust and a
fouled heat exchanger. Eventually this can reduce the life of the unit.
Before the unit leaves the factory, it is test-fired and the combustion settings are adjust-
ed. However, once the unit is installed, the airflows (air inlet and exhaust) will be differ-
ent, because of the different arrangements of the inlet and exhaust piping. This is why
the combustion settings must be re-set after installation. (For the setup procedure, see
the instructions in the following sections.)
Depending on the gas/air mixture, the burner can operate in three different ways:
• When the burner is burning correctly (correct gas and air mixture), enough air is
available to combine with the gas, and the flame produces CO
2
(“carbon di-oxide”)
and H
2
O (water). (“Carbon di-oxide” includes two oxygen atoms attached to every
carbon atom.)
• When the burner cannot get enough air, the flame is “starved” for air. The flame
continues to burn, but since enough oxygen is not available the result is CO (“carbon
mon-oxide”). (“Carbon mon-oxide includes just one oxygen atom attached to each
carbon atom.) This is dangerous because carbon mon-oxide can replace the oxygen
in the air you are trying to breathe. This is the reason for the warnings we have
included in this manual.
• Another kind of problem can happen if the flame has too much air for the amount of
gas supplied. In this case, the extra air cools the flame temperature. The flame lifts
off of the burner surface, and begins to produce too much CO.
Of course, the main concern is that bad combustion is potentially dangerous, but bad
combustion can also cause maintenance problems in the unit. A “sooty” flame can
eventually create enough soot to plug up the heat exchanger. So the goal is to set up
the burner so that it is always producing the correct amount of CO
2
, and the minimum
amount of CO. To do this, you use two adjustments on the gas valve: the high- and low-
fire CO
2
adjustment screws.
As you adjust the combustion, you will need to set the control system to the High Fire
and Low Fire conditions. NeoTherm units have been produced using two different types
of user interfaces. In the following section we have listed instructions for both types of
interfaces. Please check Section D1 at the end of this manual to identify the type of
interface used on your unit.
C1