Payne HVAC high limit switch

My furnace works for several minutes then shuts down and restarts every few minutes. I have called many HVAC pros and still has not resolved it yet. However, the last technician bypassed the high limit switch and the furnace worked perfectly. He told me to replace the limit switch. He left the switch bypassed until the part is delivered and replaced. The unit ran perfectly for a week until the part came in and got replaced. Right away, as soon as I replaced it, the new limit switch is turning the furnace on and off. What are the chances the new high limit switch is bad? Could it be something else? If so, how come bypassing it worked fine? Any help is appreciated.

 

Welcome to the forums.

First off...... NEVER bypass a high heat safety limit. Your "tech" should know better.
It's ok to test but it must be in place for unattended operation.

0 to none....... just like the original one.

You need to find out why the furnace is overheating.......
Dirty air filter or too restrictive.
Dirty blower wheel.
Dirty a/c coil.
Blocked returns or too many registers closed off.
Burner overfiring.

 

Wow. OK at least I have the new one in there now.

They checked a lot of things including changing the air filter to a cheap one that allowed more air in. They also checked other things including checking the air return. As for the blower wheel and a/c coil, I'm not sure if they did or not. When nothing worked after all that is when they recommended the replacement of the high limit switch. Bypassing it was the only thing that made it work. Its odd since it used to work fine and started doing this about a month ago. The unit is only 2 years old. I'm paying about $100 for each time they come out and suggest a fix that doesn't work.

I didn't mention earlier that it displays error code 33.

Thanks for the response!

 

clock the gas meter to make sure it's not over-fired: https://hvactechhangout.com/home/sys...k-a-gas-meter/

 

Thank you for the suggestion.
So I clocked the meter and got 28 seconds which equates to 64,000 BTU/h. My unit is rated at 60,000 BTU. Not far off?

I turned the supply gas valve just slightly to reduce the flame by about only 10-15%. I sat and waited for about 30 to see if it will stop, but it seemed to have fixed the issue. I re-opened the valve back and shutdown the unit for the night. Would it have been safe to leave the flame reduced and let it operate that way? The unit is only 2 years old and it had worked fine last winter and half of this winter so not sure what changed?

 

No, it is not safe or correct to use the gas shutoff as a throttle. You should check gas supply and manifold pressure.

 

Thank you guys. I will be calling in the professionals now that I narrowed it down. Thank you so much.