Hello thanks in advance for a help anyone can give me.. I will try and explain my problem a simple as possible... I recently went to change my parents old style mercury thermostat to a new digital thermostat. There is only 2 wires coming out of wall but the wire seems to be speaker wire so I thought nothing of it and connected one wire to the "R" terminal on the new thermostat and the other wire to the "w" terminal and everything seemed to work OK I tested it a few times to make sure it went on and off as I adjusted the temp on the thermostat anyway I get a call from my dad saying that its getting cold in the house and he tried putting the temp up on the thermostat and that heat is not kicking on but when I go and test it it works fine after a few nights like this I am baffled that it works fine when I am there but as the night goes on it stops working... he thinks that it has something to do with the speaker wire being used and not thermostat wire but when I jump the 2 wires together I get the heat to come on so I am assuming the wire it fine... any ideas please... its a forced hot air system 1 stage I believe thanks

By jumpering to 2 wires together and the furnace works, tell you the wires are good and not broken,its possible you have a bad new thermostat. What is the brand and where did you buy it? They should take it back if bought at a local box store,, get a good honeywell or whiterogers,,

Did you read the manual? Is there a clock and a setting for night temp (to not go above it)?

You need to be careful of these big box stores and their stats. Anyway, yes---- read the manual. Is there a COMMON required on this new stat? If so, you don't have enough wires. They'll take 3. Oh yes... the batteries. Do they control a clock only or what exactly is their function. You may have too advanced type stat if this is a HEAT only application. If your parents have heat and air... you definitely don't have enough wires.