Programmable thermostats for baseboard heat not working

November 19, 2023 12:08 PM

We recently bought a condo with baseboard heat, and are replacing the ancient (60s-era?) thermostats with programmable Honeywell RLV4305s. When we do so, the display starts flashing random symbols. What could be the issue?

The comments on the reddit post linked above (not made by me) say the issue is either a.) a broken thermostat or b.) a "voltage issue." Some more snowflake details:

• We tried a different unit of the same Honeywell model and had the same issue.
• I bought a cheap multimeter. When I measure the voltage on the wires for any of the thermostats (either the one that I took off in order to replace it, or the other ones through the house that I haven't touched yet), the multimeter reads 210 volts. Shouldn't I be expecting it to read 240 volts? Or maybe I'm just bad at reading a multimeter.
• The baseboard heater in one

IANALicensed Electrician, obviously, but it seems like the following could be the possible paths forward:

1. Quit being an idiot and hire an electrician.
2. Try a different programmable baseboard thermostat model. The issue here is that we don't want some wifi enabled, Internet-of-Things piece o' junk.
3. Try a much more basic non-programmable model, basically updated versions of the ancient thermostats we have.

Thank you for reading.

posted by HeroZero to Home & Garden (8 answers total)

Response by poster: Should also note: the ancient thermostats are ancient, but they are not mercury-based. So I got that goin for me, which is nice.
posted by HeroZero at 12:10 PM on November 19 [1 favorite]

Quick look at the stat says it’s not rated for loads over 14.6 amps, which, even at 240 volts, resistive heat draws a ton of current. And the fact that this is line voltage, and you’re getting slightly wonky voltage readings (although it’s not unheard of for multiple unit housing to have 3 phase 208 incoming, rather than 240 split phase) makes me say you probably want to leave this to an electrician/hvac pro.
posted by HVACDC_Bag at 12:22 PM on November 19 [1 favorite]

When I wanted to replace the 70s era dial thermostats in my apartment with baseboard heating I initially called my apartment complex to ask about it and they poo poo'ed me and told me it was too complicated to explain the voltage requirements. I ended up consulting an electrician (friend of the family) to make the correct purchase and the maintenance team was so pleased with my electrician's selection that they switched the entire complex over to that unit when they remodel units after moveouts.

I would get an electrician.
posted by MagnificentVacuum at 12:49 PM on November 19

Sounds very likely that the voltage is the problem (the amperage won't be, unless you're trying to control a number of large baseboard heaters with one thermostat). It wouldn't hurt to try a 208V thermostat (there are plenty that will do both 208V and 240V, but it looks like yours isn't one of them) as some condos do have 208V heating, as noted above.
posted by ssg at 2:39 PM on November 19

Baseboard heaters are generally 250W/ft. At 208V they pull a nominal 1.2A per foot which is a maximum of 12' per stat. As noted by SSG most spaces won't have more than that but you have to be careful with spaces like a open plan living room/dining room/kitchen which might end up with more.
posted by Mitheral at 3:22 AM on November 20

Response by poster: Thanks, all, for having the time and inclination to respond.

Am I correct in thinking that it'll be hard to find programmable 2-wire 208V-compatible thermostats?
posted by HeroZero at 6:09 AM on November 20

Try here.
posted by Ferrari328 at 6:58 AM on November 20

Here's an option from Amazon.
posted by ssg at 1:25 PM on November 20