Thermostat help

[lrothkcsa]

I'd like to begin by saying I'm a bit of a dullard when it comes to HVAC. I'm trying to replace the thermostat in my den (zone - baseboard heating). It's a thermostat like nothing I've ever seen before (looks to be quite old as well). It's a vertical rectangle with the temperature adjustment knob on the bottom. There's a yellowish faceplate on the front that says Berko, and when I remove the cover, the tag underneath reads:
Model M7-D
18 AMP / 277 VAC
22 AMP / 125, 250 VAC
Double Line Break
Mears Control Inc.

Underneath this "lid" there are two things that appear to be contacts (one black and one maroon) that say "Unimax Switch" on them.

The wiring behind it almost looks like an electrical box rather than a thermostat with thick copper wiring in (from what I can see) black and white. I've run web searches using each of the phrases mentioned and come up with nothing. I've installed a few thermostats in my house thus far, but had been hesitant to try this one because of the look. Unfortunately, the heat in my den has stopped working, so we're a little desperate. Any information on this thermostat, or suggestions on how to wire it to a newer model would be very much appreciated. We've called a couple of people in our area, but none will take the job.

Thanks in advance.

[Rewired]

Sounds like the typical electric heat " LINE VOLTAGE" Thermostat of the " 2-pole" flavour....
These can be obtained at any hardware store or home improvement store.. Also, before you go about changing the T-stat, make sure there is power present at the thermostat as well as the baseboard...
On occasion I get calls for No heat and its rare that its the thermostat but it does happen.... Usually its a dud baseboard heater, and they are cheap and very easy to replace, so are the thermostats..

A.D

[lrothkcsa]

quote:Originally posted by Rewired

Sounds like the typical electric heat " LINE VOLTAGE" Thermostat of the " 2-pole" flavour....
These can be obtained at any hardware store or home improvement store.. Also, before you go about changing the T-stat, make sure there is power present at the thermostat as well as the baseboard...
On occasion I get calls for No heat and its rare that its the thermostat but it does happen.... Usually its a dud baseboard heater, and they are cheap and very easy to replace, so are the thermostats..

A.D

Thanks for the advice - my apologies for the dumb followup, but how can we test the baseboard? I'm assuming the thermostat would simply be using a voltage meter, but wondered if it's the same with the heater.

thanks again

[suprheat]

Well there are several ways to check. First make sure you have voltage going to the heater. 120v or 240v depending on the heater - check the nameplate. If you have the proper voltage, put on an amprobe and see if it is pulling current and compare the reading to what the nameplate on the baseboard says it should be. The nameplate will tell you in watts not amps so you will have to convert your amperage reading to watts. (voltage x amps = watts). If you don't have an amprobe, check to see if you have voltage at the baseboard heater and if you do, see if it's putting out heat. If it is then it works! If you have voltage and no heat, remove voltage to the heater and ohm (check continuity) across the heater leads. You sould remove one of the leads so as to avoid false readings. Your ohm reading should again correspond to what the wattage of the heater is. (reverse the formula above and then voltage / amps = ohms). If you ohm reading is high or infinity you have a bad heating element. Good luck (kill the power when you're playing with bare wires!)

[HayZee518]

The "stat" you state is a Berko across the line controller. Line voltage will be present in the wall switchbox (120 or 240) depending on your baseboard heater.
BUT you state this is a zonal heater - THEN of course you'll need a low voltage type of "stat." Robert-Shaw or Honeywell or even Nutone might be choices of yours. Two small gauge wires are connected to this. One side is hot the other returns to the TACO zone valve which opens and closes and controls your burner and circ pump. The burner control comes off the TACO valve wiring and goes to the boiler controls.