Came home after Thanksgiving to find our heat had been down for 4 days, current outside temperature is a high of 15 F. 

Hoping to get some insight because I’m getting conflicting information and a very expensive recommendation (new furnace) with no clear explanation. Basically, it's a diagnosis of exclusion. 

**Furnace:**  
Heil Model **N9MSE0601714A**  
Installed March 2014  
95% efficiency, 3 burners  
Pressure switch: **Honeywell HK06MB012** (0.68" WC PF)

# Symptoms

* Furnace *shuts down* when the top panel is installed. Three flashes, indicating pressure switch is stuck open. 
* With **top panel off**, furnace runs completely normally for hours with stable blue flames and no rollout, noise, or visible issues.
* Pressure switch reading during tech visit: **0.50–0.66" WC** (switch rated 0.68").
* First visit - Cleared p-trap, but I found the area around it soaking wet afterwards (see last photo). 
* Second visit - Pressured dropped momentarily while running with panel on, system shut down. Same error, pressure switch stuck open. Tech leaves for the night with furnace running and top panel removed.
* Follow up, next day: Told everything was ruled out, so the heat exchanger must be cracked and I should replace the furnace. 

# Tech Findings

* They “checked everything else” (hoses, drain, inducer, trap — though they didn’t seem very interested when I mentioned recent condensate under the trap).
* **“The heat exchanger is probably cracked and letting in room air, reducing vacuum.”**
* They want to pull the heat exchanger for $1,000+ “to look at it,” or replace the whole furnace.

No visible flame disturbance, no yellowing, no rollout, no odd noises, no CO issues, and the flame looks *normal and steady*. Only occasional tiny orange flicks like normal dust.

# My Questions

1. **Does a furnace that ONLY fails with the panel on — but runs perfectly with it off — actually point to a cracked heat exchanger?** (Everything I’ve read says no; HX cracks usually cause flame disturbance, rollout, or safety trips.)
2. **Would you try replacing the pressure switch first?** (It seems like a cheap, logical step before pulling a heat exchanger.)
3. **Is it common to jump to “cracked heat exchanger” without proving it?** They did not use a mirror, camera, combustion test, or any of the usual methods I’ve seen recommended. Told only way to know was to pay $1K for them to remove it and inspect it. 

Any input would be hugely appreciated. I’m trying to avoid being pressured into a $5K replacement unless it's truly needed. Already dropped $8K earlier this year for a new A/C system replacing one that was 17 years old. 

Heil furnace only runs with top panel off. Tech says likely “cracked heat exchange", yet left with in running.