Have HVAC Questions? Ask an HVAC Expert for Answers
Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation
Are you looking to replace the Tekmar control as well as the thermostat?
Ok, first efficient thermostats is kind of a misnomer. Any programmable thermostat will reduce energy usage but radiant heat has too long of a recovery time lag to respond well to periodic set backs. So this Uponor is one good optionhttp://s3.supplyhouse.com/product_files/Uponor-A3100101-Product-Overview.pdf
If you still want a setback type thermostat the Nest is a decent choice
As far as an operating control goes by far the most cost effective, simple and efficient option is the Beckett AquaSmart.
It uses a proprietary algorithm to modulate boiler water temp without the need for outdoor sensors. It does what the Tekmar does at a fraction of the cost and complexity.
Possibly, I have no direct experience using non Tekmar components with a Tekmar controller.
You asked initially for thermostat AND control options. I gave those to you. If you had asked for a different manufacturer's stat to work with Tekmar I would not have answered since as far as I know only OEM Tekmar components are approved for use with their controllers.