Honeywell RTH230B thermostat: everything works fine, but suddenly the Fan ON function doesn't work. The fan is OK (works on Auto in Heat mode), and I put in new batteries. What's up? John

SOURCE: honeywell RTH230B

Normally, you should have 5 color wires: W-White, Y-Yellow, G-Green, R-Red and C-Blue.

The Blue wire is a common from the transformer on older systems, which is probably hooked to RC terminal.

Try this: Remove the blue wire and jump the RC to RH with the red wire and you will be fine. Blue wire should not be needed with the new thermostat.

This should also be stated in the instruction manual.
Hope this helps.

SOURCE: honeywell rth230b won't shut off heat

Sounds like a relay sticking. Possibly in the thermostat or possibly the furnace relay at the furnace. The next time it happens, unplug the thermostat from the wall. If the furnace still runs then it's the furnace relay.

Hope that helps...

Geno

SOURCE: problem with Honeywell RTH230B Thermostat

Sounds like you have it wired wrong..   Pop the top off and give me to color of the wires and tell me which letter each color wire is on.. that will tell us right away if you have it wired wrong

SOURCE: Honeywell Thermostat RTH 7500

Assumed all the wiring are correct,

to change from manual switching from heat to cool, press [system] button ( left ) to go into system setting.

then press and hold the [fan] middle button untill option display 120

use up down button to select option 300 ( Manual/Autochangeover) ,

select 0 for manual, 1 for automatic. ( read caution in page 22 of installation manual )

Good luck

SOURCE: batteries died on my honeywell RTH230B replaced but furnace won't

you will have to reprogram it according to the operating manual.
The manual is available on www.manualnguide.com