Lennox Pulse Intermittent Firing - http://www.hvacmechanic.com/ Forums
Original message
| bjwww
 |  "Lennox Pulse Intermittent Firing"
, posted Tue 11 Nov 10:06  
My Lennox Pulse furnace is more than 25 yrs. old with a good exchanger and no detectable CO. But for years now it has cut out and won't recycle to continue heating. I've had three new control modules put in it and the problem keeps coming back. The thermostat continually calls for heat, the furnace coughs and doesn't fire, several times, and (sometimes) it finally does catch and start running. It doesn't continue though. Something cuts it out (plenum overheat?)and the misfire/cough-failure-finally-firing sequence happens again once or twice until it fails and then it just sits there while the thermostat is still made. If we notice the house getting cold, I can (sometimes) get it to fire by turning the power supply off and then back on but that doesn't always work either. Most mornings we wake up to a cold house and I have to do the power off/on thing to get it to go. A new flapper seems to help; but not for long.
Beej
|
|
Replies:
|
| mechacc
| "Re(1):Lennox Pulse Intermittent Firing" , posted Wed 12 Nov 12:12
First you said the heat exchanger is good. Was the heat exchanger pressure tested per Lennox's instructions? Thismust be done every 4 years. CO alarm not going off is not an indicator that the heat exchanger is safe.
Have you a qualified Lennox technician look at the furnace?
The problem could be dirty air diaphragm holder. Many just replace the diaphragm and do not clean the holder. IMO this is a mistake as a sooty dirty holder can cause the diaphragm stick.
The gas flapper should also be removed and checked if it is frayed it should be replaced.
Vent pipe condensate drip leg debris collects in the bottom of the trap and backs up the condensate water into the vent pipe area.
Debris in the intake or vent pipe such as spider webs or mud dauber nests will cause rough starting.
Changes in burner manifold pressure. Must be checked with a gas pressure gauge or manometer.
Before replacing any more parts have the heat exchanger pressure tested.
MechAcc
|
|
|
|  |
|
