A.O. Smith BTX-100 Service Handbook page 18

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
GAS PRESSURES (CONT)
Typical manifold and supply gas pressures during:
1 Standby Mode
2 Pre-Purge Mode
3 Heating Mode
1 BLOWER OFF / GAS VALVE OFF
Manifold 0.00" W.C. Supply +9.70" W.C.
Manifold
Gas
2 BLOWER ON / GAS VALVE OFF
Manifold -6.86" W.C. Supply +9.70" W.C.
Manifold
Gas
Service Notes - Gas Pressure Adjustment
Manifold gas pressure is factory set and should not be adjusted in the field. If manifold gas
pressure differs greatly from the pressures in Table 2 consider the calibration of the
manometer being used - try a different manometer. Call the technical support phone number
on the water heater label for further assistance if pressures are considerably different.
Table 2 - Gas Pressures
FUEL TYPE
Natural Gas
Propane Gas
†. Minimum supply gas pressures must be maintained under both load and no load conditions.
Technical Literature Department
Supply
Gas
Supply
Gas
†
MINIMUM SUPPLY
3.5" W.C. (0.87 kPa)
8.0" W.C. (1.99 kPa)
Servicing should only be performed by a Qualified Service Agent
CHECKING GAS PRESSURES (CONT)
5 Open the supply gas shut off valve - restore
power - start a heating cycle.
6 The rise in manifold pressure and corresponding
drop in supply gas pressure confirms the water
heater's gas valve is opening and gas is flowing
to the burner.
7 Record the supply and manifold gas pressures
with the water heater firing.
8 Supply gas pressure should not drop below
minimum given in Table 2 below.
9 Manifold gas pressure should be within the range
shown in Table 2 below.
10 Look through the burner view port (page 11)
burner flame should be blue.
11 Shut off power and gas supply - disconnect
manometers - close test port needle valves.
12 Restore power and gas supply. Check for gas
3 BLOWER ON / GAS VALVE ON
Manifold +0.05" W.C. Supply +7.04" W.C.
Manifold
Gas
MAXIMUM SUPPLY
14.0" W.C. (3.48 kPa)
14.0" W.C. (3.48 kPa)
17 of 52
Supply
Gas
MANIFOLD
0.00" to +0.05" W.C.
(0.00 to +0.012 kPa)
0.00" to +0.05" W.C.
(0.00 to +0.012 kPa)
Ashland City, TN © 2008