Calling on HVAC furnace gurus...

Got a strange issue i've been trying to diagnose with our home furnace. Its a single stage approx 16 years old.

When the thermostat calls for heat, it goes thru the initial purge (inducer motor runs, ignitor and flame rolls out then as soon as the blower motor kicks on the flame goes out, its hard to see which happens first its almost as if they both happen at the same time.

The issue is really intermittent, sometimes it takes 2-3 cycles for the flame to stay on and it runs till thermostat is satisfied. Sometimes it starts up the 1st time and works correctly. So i thought it was the flame sensor so i changed it out in January and it seems like it fixed the issue but im not always home and paying close attention to the furnace operation but this morning it happened again and took 3 cycles to finally stay running.

No fault codes at the circuit board, I'm thinking something is starting to fail---limit switch is probably next to get changed out... What you guys think?

 

Judging by the age of the unit, the heat exchanger could be cracked, allowing air from the blower to pass through the chambers, and puff out the flame.

 

We had a furnace that did that, heat exchanger had holes burned in it.

 

Sounds like it may be time to just give the professionals a call...

 

Unfortunately, you’ll more than likely be paying for them to tell you, “It’s time for a new unit.” Just to prepare you.
Good luck

 

Curious though, wouldn't a cracked heat exchanger cause the issues more often? It's not happening everytime the furnace calls for heat

 

Depends on the amount of air flowing through the exchanger, instead of around it. Does the rollout switch trip when the unit shuts off? Or does the flame just go out?
A good way to tell is to watch the flame while the unit is running. If the flame is inconsistently dancing around, and mostly orange in color, the exchanger is cracked.

 

No its a steady blue when its on, I just had a company come out in the fall and did an inspection/cleaning and all was good, but anything could change in 6 months. I've been preparing to get it changed out in the next 1-2 years anyways. Typically the water heater, furnace, AC only lasts 15-20 years these days...