i have an old honeywell wall thermostat that appears not to work anymore . it has three wire s going into the unit blue yellow and red . there are 4 numbered connections . red is 1 , blue is 2 , yellow is 3 , 4 is unused . can i fit a standard modern honeywell dial style thermosat or digital etc . if so how do i wire the modern one up , is it compatible etc , cheers |darren