I have a Honeywell RTH230B thermostat and a Carrier 58PAV furnace. I have the TS set at 72 degrees and when it drops below that, the flame icon comes on indicating the furnace is starting so it can bring the temp back up to 72. My problem is, it will work fine like this through 4-6 cycles and then after the last successful cycle (whichever it may be) when the temp drops below 72 to say 68, it will show the flame icon on the TS but the furnace isn't going nor blower. It started doing this the last week and it has been really cold, down to 2 degrees at night (don't know if this matters) The only way to get it going again is to hit the reset switch on the furnace, which will bring it back up to desired temp. It seems to be getting worse with the cycles only reaching 72 1-2 times before the problem occurs again. I don't know if it's the TS not sending the signal to the furnace or the furnace not receiving the signal. Any clues or advice would be much appreciated. Thanks. -Trent

It sound to me like you have a furnace problem and not a thermostat problem.
If you have to reset the furnace it could be the flame sensor if so equipted.

Here is a copy of your thermostat manual just in case you do not have one.

http://customer.honeywell.com/techlit/pdf/69-0000s/69-1800.pdf

Your PAV has a diagnostic LED light that will blink a code. It is viewed through a small clear viewing port and is located just below a fuse on the circuit board. It will blink very quickly a number of times then slower a number of times. This is your diagnostic code. On the back of the door panel, there is a sticker that reads "LED Codes". This will give you a starting point as to what the issue may be.

Your PAV has a diagnostic LED light that will blink a code. It is viewed thru a small clear viewing port and is located just below a fuse on the circuit board. It will blink very quickly a number of times then slower a number of times. This is your diagnostic code. On the back of the door panel, there is a sticker that reads "LED Codes". This will give you a starting point as to what the issue may be.

I know it has the LED and it is not blinking or anything, that's why it's confusing. It is also hit and miss when the problem occurs. Thanks for the help so far.

Here is where I would start. Start by taking the wires off the TS and shorting them together the furnace should now come on if it is calling for heat.