Older Boiler Thermostat Replacement

d12341999

I’m trying to replace my very old White and Rodger’s thermostat with a more modern one (without a C wire). As I was disassembling it, I noticed the wires were thicker gauge so I got worried they were line voltage. I measured the voltage with a multimeter and came up with 21v. The thermostat also has a label that says it’s rated for max 30VAC and gives a range of 0.35 and 0.8 amps (pics of all this attached). Is it normal to see older thermostats with thicker wire in a 24v system? I’d like to splice/wire nut the thicker gauge wires to smaller thermostat wire so I can plug it into my new thermostat. Is this safe to do? I haven’t measured current to it, but I feel like it’d be within the range written on the thermostat which can be supported by thermostat wire.

ethicalpaul

Anyone that long ago could have used whatever wire they had on hand. Your meter isn't lying.

Don't try to measure current on those two terminals, you will blow a fuse, best case. Edit: Yeah this part I said was wrong—of course the current won't be a big deal if these are connected…they are connected every time there's a call for heat.

Go in the basement you should see the transformer that is powering your boiler and you can either see how it's labelled or you can measure voltage there on the secondary if you are still nervous.

Big Ed_4

And yes you can wire down to 18 gauge ..

Bernie_the_Brewer

Yes, I have seen thick t-stat wires in older houses.

Jamie Hall

Not a problem. A two wire thermostat carries almost no current at all.