There is a reset button on this thermostat in the event the keys don't respond. If the reset button is depressed it will reset only the key functions as well as the clock.

Either the button is faulty or when someone goes to make a change to the thermostat they are pressing against the thermostat and pushing the reset button.

Make sure the thermostat is PROPERLY attached to the wall and try, try again.

This may be caused by a temporary loss of power to the thermostat. Check to make sure all the wire connections are secure at the thermostat and the furnace.

It could also be a sign the transformer supplying the 24V power is having issues. If you have a voltmeter measure the voltage between the R and C terminals at the furnace and thermostat both when the furnace is off and running. A temporary voltage drop could cause the time to be lost but not the temperature settings since they are stored in non-volatile memory . If that is the case then you will need to replace the transformer.

Does it have a battery back-up (maybe a button battery).

It doesn't have a battery back-up but all I know is that in the past since 2003 it never had this problem and my mom said these kinds of things never brake since all her friends has the original thermostat still. There is a spot that looks like it's made for a battery but it's a white circle so they must of not put it in so you can put a battery. Is it possible to cut the cost so they didn't made it so it can have a battery?? We upgraded to heat pump in 2003 so we had professionals install it and they installed this newer thermostat. I didn't see if it had a reset button but I thought since it had no battery to save the settings it didn't matter but strange that all other settings like what temp my mom set in morning, day, evening, night, etc still there just the clock gets reset.

my mom said these kinds of things never brake since all her friends has the original thermostat still.

Well my mom said 'You better shop around'.

If they don't have a battery backup to save the settings, they usually have a small capacitor hat serves this functionality, albeit for less time. This lets you take the thermostat off the wall for programming, etc. It does sound like the reset circuitry is coming into play for some reason. As Mike says, it could be the transformer, but these are much more reliable than thermostats. If you replace the thermostat, make sure it's one that's designed to work with a heat pump.

My vote is a intermittent power connection or the power is dropping below 24V. It is very common for the circuit to have a power on reset function. The temperature settings are kept in either non-volatile memory, backed up by a battery, or kept temporarily by capacitive storage function. If you can borrow a voltmeter we can eliminate lack of correct voltage level as the cause.

It is unusual that an electronic thermostat would fail but it does happen. Don't invest in another thermostat until you check the voltage.

Well I did hold the reset button for a sec and put the time back but my question is how many sec was I suppose to hold the reset or was it just suppose to be a fast click on it? Thank you

Well I don't have a way to test the voltage and also it's not like we lost power recently and I noticed that since the last time one of the pros came to fix the board in the furnace now even switching the power off by the furnace didn't power off the thermostat. For years it turns the screen blank on the thermostat if I switch off the thing next to the furnace. We had a year ago a problem with the board in the furnace so they had to replace it.

The reset button just needs to be depressed, there is no need to hold it. Which means if this button rubs up against something it could reset the clock by merely making a change to the thermostat or bumping into it... or this button is failing causing the clock reset.

It could be a loose power wire connection as well, but because you weren't complaining of known power supply problems and how many times a year I see thermostats haphazardly mounted to the wall...

The magic 8 ball said: 'Yeah you could be right.'

#What's in a guess anyway?

The world may never know.

So I guess there is no really way to find out what's wrong? Well last time I pressed the reset button is when I took the face off and holded it for 1 sec but I dont know if I was suppose to redo it again with just clicking it this time without holding it. Thanks

Not unless you catch it doing it while you are standing there looking at it. Otherwise you're left with holding the magic 8 ball.

Hey wait! that's my job.