Home thermostat problems

Ok so I had a thread on here a couple weeks ago and received some very valuable assistance troubleshooting my humidifier which is coupled to furnace. Well I finally got it going (problem was thermostat) and installed a new honewell cheapo t stat heat only which controls furnace blower and wood stove boiler setup (Hardy).
Everything worked well for a couple weeks and then noticed the house was cooler than expected this morning so kicked the t stat up and nothing. Unhooked two wires from tstat and crossed and kicked on and seems to work fine. So I assume bad tstat and call my local store and they switch it out under warranty. I hook up new one and nothing. So I'm looking at contacts in tstat and notice the little contact screw looks too recessed to make connection and use pliers to turn it in a bit and unit fires up and seems to work for a couple hours until I heard some shuddering sounds as if the tsat was going on/off/on/off rapidly like an intermittent connection. So I adjusted the screw back out a bit and works a little better, but if kids run down hallway or if I tap on wall it still kicks on/off.
So my primary question is WWWWWWWTTTTTTTTTTTTTFFFFFFFFFFF is going on? What is that damn little screw for? What is the slide setting for that says 1.2, .8, .6 etc.? I have set at .8 for wood boiler stove as specified in tstat manual.
Here is pic of thermostat in next post.

 

Its actually not mercury. Just a cheap ass bi-metal $25 unit. Does not control gas heat or AC, so I went cheap.

 

sorry to hear you are having more issues. looks like you have the honeywell T1000? heat only.

 

yep and this is getting very old

 

Yall think I need to bite the bullet and spend some $ on a higher quality stat? I figured internals were all pretty similar, just difference in features.

 

Actually CT30, but yeah heat only

 

i dont know the word for it but the screw is for a setting that you have your system. they have a heat only digital stat, and that could (more than likely) be more afficient. the style you have has like a 3-5 degree diff. and the digital ones have +1/-1. <----those are pretty close.