New to me house. Drees home built in 2012, Lennox ML193UH090XP48C furnace with a Jackson Systems Z-300-HC-MS zone controller separating the first and second floor. The zone controller is repeatedly hitting the high limit and shutting down the burners. According to the dip switches it is set at 160 degrees. I pulled the zone controller probe and verified that the temp is indeed 160 almost exactly. Even after letting the system run without the controller intervening, the temp stayed around 160 +- 2 degrees. Is this ok? Other info I know:
I have a relatively inexpensive manometer on order to try and check the static pressure of the system. I suspect the ducts are undersized but I don't know if I'll be able to do anything about that. An Airtron yahoo checked the system before closing but of course said everything was normal. Probably didn't let it run very long or didn't pay attention.
- The temp probe is mounted roughly 36 inches above the heat exchanger
- The limit is tripped and temp remains constant even if both zones are calling for heat
- Also happens without the filter installed. Filter is a new MERV 8 20x25x4, I couldn't find anything less.
- All vents are open and seem to have good airflow
- The bypass damper is mechanical and is open regardless of one or two zones calling for heat.
- Zone dampers are working correctly
- The furnace limit does not trip if I pull the zone probe and let the system run continually.
- The pre-fire air temp was about 75 and the house temp was in the 60's
- The unit does have 4 fan speeds that can be selected depending on what wire is connected to the heat or cool terminals, currently it is on the medium-low speed for heat and medium-high for cool.
- Basement was finished by a previous homeowner and I'm afraid of what they've done to the duct work. I can see some of it but can't easily access it without pulling drywall.
I have a relatively inexpensive manometer on order to try and check the static pressure of the system. I suspect the ducts are undersized but I don't know if I'll be able to do anything about that. An Airtron yahoo checked the system before closing but of course said everything was normal. Probably didn't let it run very long or didn't pay attention.