Once I set my thermostat can I lock it out to prevent it from being changed? I have a Honeywell RTH4300B.

To start you have to push and hold the up and down buttons simultaneously until the screen displays "setup" across the top. There will be a number on the left, and a number in the right. Press the UP arrow until the number on the left reads 14, The number on the right should read 0. Press the DOWN arrow to change it to 1. Once this has been done you can press the RUN button to save the changes, and exit the setup screen. Your display will now read Celsius,

sounds like keypad is programmed in lock position read manual for set up to activate keypad again.

type in search bar.".download instruction manuals honewell 4300b (thermostats)"without the quote marks, you should find what you need there

May be your thermosta setting under locked. By seeing your thermostat manual release lock and then you can satrt changing temp setting or clock setting.

You have to click on the 'system' then hold the 3rd and 5th buttons on the bottom (about 5 seconds) then go down to 670, and setting 1. Repeat the process to remove lock, just change the setting to 0

With directions go to system. Then hold down 2 blanks on either side of middle for 30seconds this shows you Advanced settings . Read through and find the proper settings

It sounds like you might have the same problem that we have. I read the manual and it says that thermostat has a special lock to prevent tampering. It could be locked. If you override it only last a while and goes back to its original settings. The manual says you need to contact the person who installed it. In our case the person who was in charge when when we had it installed is no longer with the company. We don't know who installed it.

If you lost the manua, you can go to their site and download it.

Hard to help more without a model number. Sorry.

Geno

Go to www.honeywell.com and search their data base for your model of thermostat. You wil need all the numbers of your thermostat to be able to search. Once you find it, download the installation manual.
Good Luck.