[sunset_atl]

Can someone tell me the purpose of the following limit switches?

- main limit control
- rollout control
- vent safety control

Granted they measure overtemperature. It appears one looks for over temp of the air duct venting into the house, one looks for overtemp of the exhaust duct, and one looks for overtemp in the vicinity of the burner. Can someone confirm or correct. And which one is which?

From the schematic, all of these appear to be normally closed and on the same control loop. The induced draft and indoor blower motors would come on but the burner would not. I jumpered out the control loop to see if the burner would light, and it did, so I think I have one of the aforementioned sensors that is bad, but I haven't taken the time to figure out which one, so I thought I might just replace them all depending on cost. If expensive, I'll have to find my volt meter to troubleshoot. But they seem to be simple thermostat type devices - I'm assuming they can be found for a couple dollars each. Or perhaps replace them with similar open on rise button thermostat type devices. But I don't know the temperature specs or the ramifications.

The schematic also says two of the switches are "manual reset". How are they reset?

Where can I go, either online or storefront, for replacements for the above limit switches along with negative pressure control switch?

I replaced the thermocouple last year, purchasing the replacement at HomeDepot but they don't appear to carry the above items.

While I'm at it, where can I get the replacement Honeywell gas valve?

Thanks in advance.

[sunset_atl]

By the way, the model is a Rheem, RGDG 075AVER

Thanks again.

[KC13]

The main limit control is typically an auto-reset type and senses temperature near the heat exchanger. Poor airflow will trigger this one. The vent safety control can be either manual or auto reset and senses exhaust/inducer housing temperature. A restricted secondary heat exchanger will trigger this one. The roll-out limit is almost always a manual reset type, senses temperature in the burner vestibule area, and if it trips open you probably have a failed primary heat exchanger. You will likely require the services of a professional for anything beyond the main limit scenario.