'Your system is dangerous, replace it today': get a second opinion
The California contractors board describes exactly this: a simple inspection or modest repair that turns into a complete replacement costing thousands, including a case where a technician claimed a cracked, CO-leaking heat exchanger, disabled the unit, and an independent inspection found it working properly.
What is probably happening
- The claim may be true. Heat exchangers do crack, and a cracked one can put carbon monoxide into the house. The point is that it can be shown, not just said.
- Or it is the oldest upsell in the trade. The tell is urgency without evidence: no combustion readings, no photo of the crack, and a financing form on the table.
- A technician who red-tags a furnace should be able to show you the crack on a camera scope and a CO reading from a meter.
Do this in the next five minutes
- Ask to see it. A crack on an inspection camera, a CO reading at the supply register, the measurement that failed. Photograph what they show you.
- Ask for the diagnosis in writing on their letterhead, with the readings.
- Pay the diagnostic fee and let them leave. Do not sign anything today.
- Call a second licensed contractor for a diagnostic-only visit. Do not tell them what the first one said until they have looked.
- Meanwhile, if it is winter and the furnace is off, use space heaters safely, not the oven.
Do not
- Do not sign a replacement contract or a financing agreement on the day of the diagnosis.
- Do not let anyone disable the unit without a written reason. If it is genuinely unsafe, the written reason costs them nothing.
- Do not let a scare skip the second opinion. A diagnostic fee of $100 to $250 is cheap insurance on a $7,000 to $20,000 decision.
Who to call
A second licensed HVAC contractor, diagnostic only
Only another licensed technician can confirm or refute a heat exchanger or compressor diagnosis. Tell them up front you want a diagnosis, not a quote.
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What it should cost
$100 to $250
Service call or diagnostic fee, national range. Replacement, if truly needed, runs $5,000 to $28,000, with $7,000 to $20,000 typical for central AC plus furnace in a 2,000 sq ft home
Source: Angi, HVAC repair cost, updated August 2026, and CBS News, new HVAC system cost, May 2026. View source
National published range, not a quote for your job. The full cost table for this trade is on the hvac page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- What specific readings or images led you to replacement rather than repair?
- Can you show me the crack on a camera, and what was the CO reading at the registers?
- If I get a second opinion and they find it safe, will you put your diagnosis in writing anyway?
- What is your state license number so I can look it up?
End the call if
- A replacement quote on the first visit with no diagnostic readings shown to you.
- A suggestion that you borrow from a lender they recommend, or a discount that expires today.
- The unit disabled or a part removed with no written safety finding.