Trane TR250 Service & Installation Manual page 56

56
TROUBLESHOOTING
Figure 28:
Code Fault
Flame Present
with Gas Valve
not Energized
HF
Water pressure
switch fault
LO
Vent pressure
switch fault
(applies only
if indoor
installation)
Temperature
limit switch
fault
Diagnosis Step
1. ICB is defective
2. Gas Valve is defective
1. Verify that the pump is
running.
2. Verify that water fl ow
is adequate
3. Check for faulty wiring
or connection.
4.Verify state of water
pressure switch contacts.
5. Ensure that low pump
pressure does not exist.
6. Check for correct water
pressure switch setting.
7. Water pressure switch
is defective
1. Check for faulty wiring
or connection.
2. Verify state of vent
pressure contacts.
3. Check for restricted or
blocked fl ue.
4. Vent pressure switch is
defective.
1. Check for faulty wiring
or connection.
Remedy
Using the sight glass, check to see if the fl ame is present in the
unit. If not, replace ICB. If fl ame is present, move to next step.
Without disconnecting the valve from the wiring harness, use
a voltmeter to determine if 24 VAC is present at the gas valve
connections. If so, replace ICB. If not, move to step 3.
Replace Gas Valve
This is a normal display when the pump is off. Turn pump on.
LO code should clear. If LO does not clear, proceed to step 2.
Verify that water fl ow rate to heater is above minimum
required (25 GPM for TR250 and 30 GPM for TR400). If OK,
proceed to step 3
Inspect water pressure switch wiring. Ensure wire harness
terminals are securely fastened to spade terminals on water
pressure switch. If OK, procced to step 4.
Remove wire leads from water pressure switch and measure
continuity across water pressure switch with the pump
running. If open, proceed to step 5. If closed, LO code is not
caused by water pressure switch fault. Reconnect wire leads to
water pressure switch.
Clean fi lter or clear blockages. Check position of valves in
plumbing system. If OK proceed to step 6.
Adjust water pressure switch setting as shown on page 35 of
Installation Manual (only if heater is above or below water
level). If LO does not clear, proceed to step 7.
Replace water pressure switch.
Inspect vent pressure switch wiring. Ensure wire harness
terminals are securely fastened to spade terminals on vent
pressure switch. If OK, proceed to step 2.
Remove wire leads from vent pressure switch and jumper leads.
Operate heater. Measure continuity across vent pressure switch.
If closed, LO code is not caused by vent pressure switch fault. If
open, proceed to step 3. Remove jumper from wire leads and
reconnect wire leads to vent pressure switch.
Ensure that fl ue is not blocked or restricted. See indoor vent
sizing requirements in installation manual. If OK, proceed to
step 4.
Replace vent pressure switch.
Inspect temperature limit switch wiring. Ensure wire
harness teminals are securely fastened to spade terminals on
temperature limit switches. If OK, proceed to step 2.