Why am I tripping my roll back switches without roll back? The top of the furnace gets too hot to touch. My guy just replaced the burner tubes and propane release switch. I'm tired of trouble shooting on my dime!! Help

 

What’s the model number of the furnace?
Getting hot means your not drafting correctly. What is gas pressure? Has it been fully converted for LP duty, if your burning propane?

 

Model number is GMH950904CX. It's a new house build with new furnace 11 yrs ago. There is no roll back. Pressure was checked today and it was at 12 which he said was ideal for LP.

 

It's called roll out. The flame rolls out of the burner box.

If the furnace is not overfiring then it is not moving enough air to cool it. The next step is to measure the incoming(return) air temperature and the outgoing(supply) temperature and see if the difference between them falls in the heat rise allowance listed on the ID tag. .

 

Rollout tripping is caused by a combustion problem -> venting/heat exchanger/inducer fan.

Primary high limit tripping is caused by the air side getting too hot due to low airflow or furnace being over-fired.

Run the furnace and see if the flames get pulled into the heat exchanger tubes.

Monitor them when the blower comes on - if they change and you get rollout, the heat exchanger's bad and needs replacement under warranty.
You pay labor but it's worth while on a unit of this vintage.

This is a timed 2-stage furnace so you need to wait up to 12 minutes for it to kick into high - the problem may only be on high. It may be locked on high fire to begin with - depends on the dip switch settings.

A combustion problem can be diagnosed by a tech who uses a combustion analyzer. There's the incoming gas pressure, but they really need to check exhaust monoxide, oxygen, and temperature as well. The pressure can be right but it could have the wrong orifices for propane or another issue.

Right now it sounds like the guy is just guessing.

 

He came back today because its tripping the other rollout switch now. He pulled off some water drain lines today and they were plugged with this black soot looking stuff. He went out to check the vent pipe and it's all black looking out there too. Now because it still shows no sign of rollout he thinks the heat exchanger is probably plugged with the black soot as well.....which might be causing the problem of overheating the area around the rollout switch...

 

A correctly adjusted furnace should not produce soot. I think it is time to get a real service company that is schooled on "propane" as a heating fuel in to do the service and to check all previous work.