Htp uft rh wire

jdavis123

So I just moved into a new house and wanted to switch out the thermostat for a nest. My boiler is a UFT htp-80 unit. My nest keeps giving the fault, no power detected on rh wire. I looked in the manual and it seems like these only put out a 5v signal? Has anyone connected a 24v thermostat to one of these before? Our old thermostat ran off batteries so I think the previous installer never checked to see if it was actually getting power. A real, "diyer" house.

Jamie Hall

Here we go again. The Nest -- and others of its kin -- require three wires from the boiler. They are usually red, white, and yellow. Yellow is a common return to the 24 volt transformer, and red is powered. White is the switched lead. In two wire installations a third wire is not needed, not is power of any kind -- the thermostat is a simple switch, though responsive to temperature.

Your old thermostat didn't need power from the boiler to operate.

You will need to identify which wire is red power at the boiler, and which is the switched lead -- and you will need to pull a third wire for the common return, assuming that there aren't more wires hiding in the wall.

I believe that there are also wall wart accessory power supplies which can also be used.

Ironman

You don’t wanna use a Nest (or any setback stat) with the UFT. It’s a modulating boiler and using a Nest is counterproductive to the logic of the boiler’s control system. It will actually be less efficient, less comfortable, and will cause the boiler to short cycle decreasing its life expectancy.

Use a standard thermostat with the cycle rate set to 1 per hour and leave it at one temperature.

Nest is for the birds, not boilers.

pecmsg

jdavis123 said:

So I just moved into a new house and wanted to switch out the thermostat for a nest. My boiler is a UFT htp-80 unit. My nest keeps giving the fault, no power detected on rh wire. I looked in the manual and it seems like these only put out a 5v signal? Has anyone connected a 24v thermostat to one of these before? Our old thermostat ran off batteries so I think the previous installer never checked to see if it was actually getting power. A real, "diyer" house.

Your first mistake was listening to the marketing BS of NEST.

Listen to @Ironman s Advise. Its spot on!

Jamie Hall

Allow me to amplify a little on @Ironman 's and @pecmsg 's comment -- with which I agree completely.

The Nest -- and it's occupancy sensing kin -- were designed for, and operate well with, forced air heating and air conditioning systems. They were not designed for any other type of heating system, and they do not work well with them unless they reprogramed to disable all their smart features (which can be done, although not easily) -- at which point you might as well have bought a regular thermostat for about $40.

If you do really want a Nest, that's your choice, but be aware that unless you do manage to completely defeat all of its occupancy sensing and time based setbacks, your nice boiler will not perform as expected, as its controls and the Nest will constantly be fighting each other. At best, expect higher fuel bills -- perhaps as much as 10 to 15 percent higher.