What is the difference between resistance and switched live?

[Mr Hoops]

I want to upgrade our existing analog room thermostats to digital, however, a bit of research suggests our current UFH controller, a Uponor C35 uses resistance-based control and therefore to go digital will need a whole new control board that uses switched live.

Are there any heating/electrical experts on here able to explain the difference between resistance-based control vs switched live control?

Many thanks, Hoops.

[biggiles]

"Resistance-based control" sounds like a thermocouple? i.e. the device on the wall is a temperature-sensitive resistor, connected to the control unit. The control unit therefore knows the temperature in the room and can switch on/off.

Is that how yours works? Is the temperature set on the control box?

Are you trying to replace it with something like Tado?

[No ideas for a name]

Mr Hoops said:

I want to upgrade our existing analog room thermostats to digital, however, a bit of research suggests our current UFH controller, a Uponor C35 uses resistance-based control and therefore to go digital will need a whole new control board that uses switched live.

Are there any heating/electrical experts on here able to explain the difference between resistance-based control vs switched live control?

Many thanks, Hoops.

I am going to guess a bit and think that the thermostat either gives an analogue value representing the temperature - via a varying resistance, or the switched live type that would just be on or off depending on if you are above/below the set point.

For proper control surely you would want a variable ie. actual temperature, rather than on/off.

[Mr Hoops]

Thanks chaps. That is what I feared.

The wall stats are 24v two-wire controlled a dial that appears to be a potentiometer for temperature control. The control unit has a normal and eco mode so I guess it uses the resistance in the individual stat to approximate the temperature and call for heat if it falls below a set threshold.

I had hoped to upgrade to a digital system (via a Shelly switch) for more control but this is a non-starter unless there is a wifi/Bluetooth variable resistance switch out there.

[biggiles]

You could probably replace that with a Tado setup DIY in under an hour... (or other equivalents).

Unless you have millions of thermostats, it's not much more complicated than most houses.

[119]

We had a similar issue with a warm air unit, in so much the thermostat was a thermistor and count be replaced with a standard room stat.

I also seem to remember it had 1-6 or similar rather than degrees on it.

[Mr Hoops]

Quick update for anyone who comes across this thread in the future.

Decided to rip out the Uponor control unit entirely and put in a custom system using Shelly devices (similar to this guide - https://shelly.guide/application-guide/underfloor-... Temperate measurement is via Shelly H&T's which can be placed anywhere thereby doing away with the wall stats completely.

Being Shelly it all links seamlessly to my Home Assistant setup for remote access and scheduling.