Honeywell thermostat replacement

[sheep21]

I need to replace our Honeywell CM721, I believe the modern replacements would be either Honeywell T3R or T4R, is this correct and would the receiver also need replacing or would the T's mate up to my original Honeywell receiver?

 

[ShaunCorbs]

They still sell the 721s so quick swap or you can upgrade to as you say t3 but you will need to swap the receiver and wiring etc