Thermo Pride Gas/Propane Furnace Induced Draft Highboy/Counterflow/Horizontal MHA1 - Manual (Page 50)

All installations and services must be performed by qualified service personnel.
47
Yes
After gas valve opens,
do the burners ignite?
No
Check gas supply. Open all
manual gas control valves
serving the unit.
No
Correct low line voltage
problem or replace ignition
control module.
No
Measure gas supply pressure
at inlet to gas valve. Is it at
least 4.5" W.G. for natural gas
or 11" W.G. for L.P. gases?
Yes
Is ignitor positioned
correctly?
Yes
No
Reposition to
correct location.
Yes
Yes
Check for blocked or severely
corroded burners or burner orifices.
Clean or replace as required.
Measure supply & manifold
pressures. Are they constant
over time and within the allowable
ranges?
Yes
Yes
Measure voltage on the
circulating air blower
terminals "CIR N " &
"HEAT". Is it 120 VAC?
Yes
Does the circulating
air fan come on
when energized?
Does blower wheel
spin freely?
Yes
Is blower motor capacitor
working properly?
Yes
Replace Motor
No
No
Replace blower
motor capacitor
No
Check for blower wheel
rubbing against housing
or motor shaft spinning
freely. Adjust or replace
as necessary.
No
Check DIP switch settings on
ignition control module against
those on connection diagram.
Is blower still inoperable after
time delay with DIP switches
set correctly?
Do burners stay lit
past proof of flame
check?
No
Yes
Does the ignition control
module energize the circulating
air blower after the 45 second
time delay?
No
Yes
No
Check wiring to blower. If okay,
replace the ignition control
module.
Adjust supply pressure to
4.5" W.G. for natural & 11"
W.G. for LP gases. Adjust
manifold pressure to 3.5" W.G.
for natural gas or 10" W.G. for LP
gases. If gas pressure fluctuates,
a pressure regulator may be
required or gas piping
may be too small for flow.
Check ignitor voltage.
during 20 second warm-up,
it should be at least 105
VAC.