Burner Shutoff Issue - FHA Furnace

[vg92]

I have an 11-year old system with forced hot air furnace manufactured by Comfortmaker. It’s a second zone unit located in the attic of the house that I recently purchased. During home inspection, the inspector refused to test the furnaces after checking out the air conditioning function. His reason was that doing so will crack the heat exchangers.

Anyway, the A/C had been off for a while so yesterday I turned up the thermostat to test out the furnace. Air came out of the vents but no heat. I took the cover off and saw what happened. At first the draft inducer was running, next the spark/pilot was lit, and then the burner was on for about 2 to 3 seconds but immediately shut off. The furnace would repeat this sequence another time before stop trying. It appeared some anomalies were detected by certain sensors. The draft inducer kept running, although it made a scratching noise when operating. Not sure if this had anything to do with the issue.

Before I call a HVAC guy to look at it, I’d like to get a rough idea what is the likely cause of this. Don’t want to get charged for parts that are not really broken. Thanks for any help in advance.

[BaldLoonie]

A tech needs to check out the firing problem.

But you sure had a maroon of a home inspector, as my avatar would say.

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[Mr Bill]

Don’t want to get charged for parts that are not really broken. Thanks for any help in advance.

You have been watching to many TV News Investigation shows. Believe it or not, there are still some honest companies out there.

[beshvac]

A tech needs to check out the firing problem.

But you sure had a maroon of a home inspector, as my avatar would say.

Sent from my HTC VLE_U using Tapatalk 2

I actually wouldn't start a furnace in an attic during the summer where possibly:

1. The house has been empty and the AC is turned off
2. It's 80+ degrees in the house.

I had a home inspector start my infinity hybrid systems in heating mode on a 95 degree day and wrote on the ticket "systems not responding to controls"....Thank god they were protected from his **mb ass

[BaldLoonie]

If the attic was 140 and the house 90, I might be leery of firing an attic furnace or at least letting it run more than enough to know it fires.

But that wasn't his reasoning at least as conveyed to the buyer:

During home inspection, the inspector refused to test the furnaces after checking out the air conditioning function. His reason was that doing so will crack the heat exchangers.

How will firing a furnace after the cooling has been on crack a heat exchanger?

[vg92]

I did some tests with a voltmeter. When the thermostat called for heat, the voltage across the 24V and 24 GND leads on the ignition module (Honeywell S8600M) was around 25V. After the main burner was firing for 2- 3 seconds and then shut down, the voltage across the leads dropped to zero. This obviously indicated the power was cut off from the main fan control board (Honeywell ST9120C). So does that mean the fan control board is bad or it detected something malfunctioning such as the pressure switch, limit controller, etc.?

[motoguy128]

How will firing a furnace after the cooling has been on crack a heat exchanger?

Unlike you, he must be a expert in metallury, and determined that the sudden thermal shock of heating the iron from 50F to 480F as opposed to 70F to 500F was more than the metal could handle and it would crack.

Myabe he confuses air with water, and it thinkig it would be somehow like runnign a coiler without water in it then turning on hte fill valve while it's cherry hot. SOmehow I don't think it's the same thing. Boiler go boom if you're unlucky.

[BaldLoonie]

If the heat exchanger is in the supply air, Houston has a problem

[catmanacman]

On new installs I start the furnace to adjust the gas pressure in 80+ degree houses never cracked a heat exchanger. I recommend to people to hire a hvac contractor to do a pre buy inspection on home purchases in my opinion home inspectors should also recommend it as it is the most expensive appliance in the house . Call a hvac contractor to come fix it and give it a complete tune up