Pilot lights but goes out intermittently
1. Observe pilot light with front cover removed. Any yellow
indicates a plugged pilot air filter. A yellow flame is weak, tentative,
lazily drifting, without continuous bearing on thermocouple tip.
Solution: Take a deep breath and blow out the obstructed pilot
air filter or use compressed air.
In restaurants, due to grease in the atmosphere, the standing pilot
orifice can get plugged and not emit any gas but the observer does not
notice because the subsidiary pilot emits an aggressive torch. Cover
the subsidiary pilot orifice with your finger and push in on the gas
valve to test if the standing pilot is emitting gas.
2. A neglected heat exchanger will experience distortion in the
copper fin tube area, which eventually will plug the flue gas path
causing flame roll-out and partially melting the fusible link,
resulting in pilot outages. If the fusible link melts completely,
the pilot will not hold at all.
Solution: Examine the grey plastic insulation covering the fuse
wires, especially where it is parallel to the bottom lip of the
combustion chamber. You might find evidence (charred plastic) of flame
roll-out, which needs to be corrected before any parts are replaced.
3. Perform the Drop-out test. With the front jacket removed from
the heater, set your stop watch, blow out the pilot flame, and time how
long it takes for the magnet to release. You will hear a click.
Twenty-five seconds is normal.
Three components are responsible for pilot flame outages: thermocouple
(usually lasts 10+ years), magnetic valve (only a problem after its
disturbed; do not disturb it), or fuse circuit fusible link (usually the
part that we replace). Through the process of elimination we will
determine which part is at fault.
4. Gas control valve assembly is not in calibration. Call office
Pilot lights but goes out as soon as I stop pushing on the gas valve
This is a fun one. From right to left you
should have the standing pilot, then the thermocouple, then the white
enamel electrode, then the subsidiary pilot. Is everything in the
So the problem is more serious. Through the process of elimination, we
will discover which part is the problem.
First locate the small 10 mm metric nut at the cold end of the
thermocouple. Loosen the nut and pull the thermocouple out of the
magnetic safety valve.
the clear plastic wire harness (fuse circuit) and wiggle it out of the
magnetic valve. It is inserted into the magnetic valve right before the
thermocouple. Using a piece of bare copper wire, make a jumper and
insert it in place of the wire harness. Insert the thermocouple nut and
tighten to snug. Return to the lighting instructions and
see if the pilot will now stay lit.
Do not operate the heater in this jumpered mode, this is only a
fuse circuit appears to have failed and needs to be replaced, BUT
it will fail again if the CAUSE of the problem is not addressed.
Possible causes: negative pressure in mechanical room, causing flame
roll-out; flue path plugged at fin tube area of heat exchanger; mineral
build-up in coil causing overheating.
the above steps have eliminated the fuse circuit as the culprit, then we
replace the thermocouple.
If the fuse circuit and the thermocouple are not the cause of the pilot
outage, we remove the magnetic valve and check that the valve is
composed of three parts: a brass electromagnet, a white plastic housing
with a spring-loaded rubber plunger on the end, and a rubber washer. The
white plastic assembly snaps onto the brass magnet. Be
sure that the rubber washer is not caught between the brass and the
white plastic as this creates a gap that prevents the
magnet from grabbing its contact.
magnetic valve is out of the heater, we can test its working as well.
Insert a jumper and a good thermocouple and compress the plunger while
putting heat to the thermocouple tip. After 15 seconds of heating, the
plunger should stay compressed. Remove the heat source from the
thermocouple and after the thermocouple cools for about 25 seconds, the
force of the spring will release the plunger. Anything else is not
Here we are at the end of the road. The pilot will not hold and we have
done all of the above. Lastly we will be concerned with the calibration
of the gas control valve assembly. The gas control valve assembly turns
about 180 degrees between stops. In order for the valve to be out of
calibration the valve must have turned beyond its stops, which is
possible if the piezo igniter has been removed or if the gas knob
connector has been broken or removed.
Re-calibrating the gas control valve
1. Loosen the set screw on the gas knob connector.
2. Pull the plastic knob and gas knob connector off of the
splined gas valve spindle.
3. Turn the spindle clockwise until you hear gas escaping from
both pilot tubes without pushing in.
4. Turn the spindle counterclockwise until the gas stops
escaping. Find the friction point at which the gas comes on and goes
off. Retard the spindle by turning counterclockwise
slightly (10 degrees) from the friction point.
5. Place the plastic knob and gas knob connector onto the spindle
in the position where the spring-loaded arm on the gas knob connector is
barely making contact with the piezo igniter prior to
6. Tighten the set screw and light the heater normally.