I had a new Payne furnace model PG8MAA042090 installed a couple of weeks ago. It has not worked consistently since it was installed... keeps shutting off. Incidentally, we replaced the thermostat at the same time with a Honeywell programmable model. One company came out and replaced the limit switch which thy claimed was faulty but that did not solve the problem. Another company came out and said that the ductwork in the house was insufficient (spider ductwork) causing the newer furnace with more sensors to overheat and shut off. All of the vents are open and the filter is brand new. Could it be the thermostat? A faulty furnace? Or could it really be the ductwork (which was sufficient with the old furnace)? Before I invest in new ductwork, I want to rule out all other options.

If the people that installed the new Payne were real professionals they should have known up front if the ductwork was not up to par,, not being there its hard to say without looking at it, can you try and tell us about the duct system ,how many legs on the spider, what size are the ducts, size of the trunkline, how many returns, and how big are they,, someone might can give you an idea

Have a manual D done On Site. It is just about the only true way to find out if the duct work is to small for the system. A minimum number of square inches is necessary for each furnace size. The other option is to guess and that did not work so well the last time as you are finding out.