Heater runs when thermostat disconnected

[AMHoult]

Hello!

We are having propane heater issues with our 2008 Hideout. The furnace runs constantly with the thermostat disconnected but when we replaced the thermostat with a new one (same model), we get no heat at all. The slider switch can bet set to its max and even if it's 50 degrees the heater will not come on. There is no access panel to see the wiring inside the wall and we don't see a way to get to it, other than trying to take the shower walls apart.

Any ideas?

[chuckster57]

There are usually 4 wires that go to the furnace
12V Positive
12V ground
Signal to thermostat
Signal From thermostat
You may need to know the above if we have to look at the furnace connections.

You need to make sure the correct wires are connected at the thermostat. It should get its power send signals through the control box in the return duct of the AC. Remove the ceiling assembly and look for the control box. It should have a wiring diagram or at least the connections should be labeled. Start there and verify that all the correct colors are attached at the right connections.

[AMHoult]

The furnace thermostat is a separate system from the A/C (a/c controls are on the ceiling; heat thermostat is on the wall and controls heat only). There are only two wires on the furnace thermostat. It's a Suburban furnace and thermostat and only has a slider switch.

[chuckster57]

Ok. If you removed the thermostat and the furnaces keeps running you need to locate the wiring at the furnace.
Refer to above, and locate the two thermostat wires. Disconnect one or the other, if the furnace still runs then you probably need a new control board. If the furnace stops, then you probably have a “short” in the thermostat wiring.

You should have 12VDC on 1 of the thermostat wires and the other shouldnt. When you operate the thermostat the “circuit” is completed sending 12V to the furnace control board. When the set temp is reached, that 12V “signal” is broken.

[chuckster57]

Can you post a picture of the wires at the thermostat and the furnace?