Hope someone can spot what I've missed. The issue started after igniter replacement. When the gas valve turns on, sometimes ignition occurs, sometimes not. Ignition may fail on a first or 2nd strike, then ignite on the 3rd. Other times the furnace trips out. When I reset the controls, same thing repeats. In effort to resolve, have confirmed the igniter is properly positioned, confirmed that safety circuits and sequencing are correct. Confirmed gas manifold pressure is correct (3.57 WC). Burners and manifold were removed and fully cleaned (including orifices). When the unit is attempting to start, It seems as if an inverse air current may be sometimes preventing gas from flowing though the burner tube to the igniter. If I "help" the gas flow by blowing gently toward the burner tube (toward the igniter) as the gas turns on, ignition occurs perfectly every time. It seems that gently blowing air in the correct direction allows the gas to overcome whatever may otherwise prevent it from passing correctly through the tube. Since it's a high efficiency furnace with enclosed burner box, I can't imagine where the spurious airflow may be originate (or is it an incorrect diagnosis?)

 

Hoping someone can ID what this DIYer has missed - have maintained and repaired this unit for ~15 years with nothing similar before. The furnace began intermittent ignition after I replaced a failed igniter. The furnace was running normally before the igniter failed. It may ignite on any of the 3 tries, or trip out. If I remove the burner box cover and blow gently (toward the burner tube and igniter) ignition occurs perfectly every time. It seems as though there may be a reverse air current that prevents gas from flowing through the burner tube to the igniter - just my gentle blowing when the gas valve opens overcomes it.

In effort to resolve: 1) Confirmed proper igniter placement 2) removed and cleaned burners and manifold (including orifices) 3) confirmed proper manifold pressure (manometer reading 3.57 WC) 4) confirmed proper startup sequence and safety circuit operation. There is no other issue besides inconsistent startup - once it does start, it runs full cycle and heats the home as it should.

 

Welcome to the forums.

The board has been having a problem with duplicating threads. Normally we just delete one. However.... your two threads were not identical which means they may not both have the same information.... so I combined them.

I've been seeing problems with "crap" furnace igniters. They DO NOT glow as bright as the ones they are replacing which is the first giveaway. Most igniters have a slot in them where you can slide them. Try sliding it more towards the ignition port. The ignition port is the hole or slot in the burner where the gas escapes towards the igniter.

Notify the place you purchased the igniter and tell them that the burner is not always lighting. Typically they will send you another igniter no charge.

 

Make sure the gasket around the igniter is intact and in place - air leakage around the igniter can cause problems.

It is very possible the new igniter just isn't getting hot enough - possible it was designed for a longer warmup period or is defective.

This furnace does have a defective heat exchanger design - plastic coating de-laminates and blocks the secondary, causing very high co production - then it rusts out. The furnace needs to be watched as it ages.
Symptoms - water leaking into blower compartment, very hot burner box cover - bottom and top (normal for sides near flames to get hot), bad exhaust smell, high pressure drop across the heat exchanger (check with your manometer).

Failed secondary heat exchanger may not cause this problem, just thought i would mention it.

 

Thank you User 10. My problem turned out to be that the replacement igniter element positions a bit too far from the burner tube outlet. Ignition gas was going past it. I think turbulence from my blowing on was enabling ignition.

I was able to release the retainer on one side and tilt the igniter enough toward the burner tube that I'm getting consistent starts now. The ceramic base still completely blocks it's mounting opening (safety point). I lost one igniter that titled too far and grounded on the furnace frame - now have a small sheet metal screw installed - used as a wedge to retain position of the ceramic base. I've check the part numbers and confirmed that the replacement igniter meets Carrier spec. The element does seem narrower that the prior installed, but one would think the replacement shouldn't have the issue to begin with.

 

When replacing an igniter, it's best to use the oem or generic clone directly approved to replace the oem so it is in the right position without having to make any modifications.

 

Yes.... it is recommended to get the OEM replacement but that is not always possible for an end user.
Most customers don't have the access to the true OEM parts companies and the other companies that do sell to the public state OEM but are selling copycats.

I always recommend to have a spare igniter on hand. It's not if it will fail..... it's when.

 

A generic igniter specifically listed to replace the oem number is fine - what's problematic is just buying any igniter that physically fits and trying to use it.