I took the faceplate off the Honeywell unit to replace the batteries. How do I get the unit back together?

At least two free manuals are online, that might suggest how to change the batteries. I could not reach the manufacturer web site, that was reportedly under maintenance, but you might need to contact the manufacturer for assistance if the manuals don't help.

https://www.manualslib.com/manual/69881/Honeywell-Rth230b.html

http://homeappliance.manualsonline.com/manuals/mfg/honeywell/rth230b.html

Honeywell Programmable Electronic Thermostat Installation and User Guide...

So your saying the furnace will not shut off? If you take the thermostat off the sub-base will the furnace shut off? If the furnace does shut off with the thermostat disconnected from the sub-base then you have a bad thermostat

Make sure the breaker was turned back on. Make sure the batteries are installed correctly. Make sure the batteries are good. Make sure the face plate was pushed back on tightly. Wait 5 minutes for the default time on the t-stat to time out before any thing works.

This unit doesn't require a battery. It runs off the 24v from the unit. Check that your transformer is still working. Check the control board for 24v pwr. and main pwr. Check your breaker to the unit. It could be as simple as a bad stat too. You can check by using a jumper wire and jumping across from r term. to y term.

I pressed the reset button in error and the display just would not return o no heating or hot water. Nothing tripped on the board and all wires and the unit itself showed power coming through.I got it working again by sheer determination.

What I did
I took the unit from the base plate and opened the front panel to see circuit board. It has 4 clips and it all goes back together easily.

What I did.Time taken 15 minutes.

The tiny rubber reset button was collapsed, perhaps maintaining the 'off' situation.

I moved a tiny wire from touching the side of the battery.Perhaps not important but it didnt look right.

When i remounted the unit it lit up beautifully.

So the solution lies in 1 or all of these 3.
If it happens again I will try

1. simply remove the unit from its base plate and remount to see if that is all it takes.

2. Open the front and check the reset button isnt collapsed and stuck.

3. Just move that little wire from leaning against the battery -(least sure of why this might help)

hope this might help someone else

Catherine - a determined blonde lady

PLEASE FIRST CHECK THE FACEPLATE TO HEAD UNIT CONNECTIONS (WHERE THE FACEPLATE CONTACTS THE HEAD UNIT ).
THEN IF U ARE SATISFIED ,REPLACE THE ENTIRE RECEIVER.

you can send it to http://horizonwirelessonline.com
we are cellphone repair specialists - cost is about $40 + shipping - and we can even give you the official D&G firmware too.

dude im real good at this stuff and if u dropped it once ur lucky it still worked but if it dont work now ur definitely going to need a new one...

The problem is not the faceplate for any of you, it is inside the main unit. If you know how to solder, you can fix is very easy. First take the top off the unit, there is 1 screw in the back middle. Then take the CD player out. It has 2 screws holding it in at the front corners at the bottom of the CD deck. Use a number 2 phillips and take out the gold screws holding the CD deck in place. Then you can pull out the CD deck, and be careful not to damage the ribbon cable connected from the CD deck to the main board. The deck can just sit up and over to the left to get it out of the way for what needs to be soldered.
Look inside the main unit on the board and you will see in the front right corner a series of surface mount resistors all connected in series. Just reflow that solder on them with a small amount of new solder added and the display will once again work perfectly. That solder is very heat stressed, that is the problem. I have fixed dozens of these over the last few years. Make sure you put it back together the same as it came apart, and you are done.

Typically if you have a yellow wire in the "y" terminal blue is used as common or "c". As far as your jumper from rc to rh, that will depend upon what type of heat you have. If all of your heat and cooling come from your packaged unit outside, yes you will need the jumper. If this does not work maybe you have a bad breaker or transfomer.