17
RHT
Series
Check that gas pressure is within
minumum and maximum inputs
as indicated on the heater’s rating
plate. Is gas pressure ok?
No
Differential switch may be faulty or there
is a restriction in the exhaust or intake.
Correct problem.
Yes
Check the gap
on the igniter.
Is the gap between
1/8 in. and 3/16 in.?
Adjust gap.
No
If heater does not enter high fire mode, check the following:
Is there 24VAC across
the red wire on the
relay board and ground
on the circuit board?
Check for 24VAC across the
COM and HIGH on the 24VAC
terminal. Is there 24VAC?
No
Yes
Repair or replace faulty
wiring or thermostat
Replace
relay.
Replace
gas valve.
Yes
No
NOTE
: To confirm the heater is not in high-fire mode, check the manifold pressure (3.5 inches W.C. natural gas or 10
inches W.C. propane gas). If the indicator light is not illuminated, it is faulty and should be replaced. If the manifold
pressure ranges from 2.3 to 2.8 inches W.C. natural gas (model dependent) and 6.0 to 7.5 inches W.C. propane gas
(model dependent), the heater is in low fire mode and the troubleshooting steps described below should be followed.
Were the gas lines
purged of air?
Yes
No
Purge gas lines.
Check for damaged
insulation or loose
terminals on the
high voltage spark wire.
Is it ok?
Is the differential
switch in the
closed position?
Differential switch may be
faulty or there is a restriction
in the exhaust or intake.
No
Yes
Yes
Electrode sensing may be
faulty or flame signal may
be weak. Check that heater
is operating at proper gas
pressure as indicated on
the rating label. Clean or
replace electrode if needed.
Check the spark
electrode. Is the
ceramic cracked
or loose?
Yes
Replace electrode.
No
Replace.
No
