DIYbanter - View Single Post

Jerry Peters

wrote:
Last night it began getting cold in my house. I went to the thermostat
and found out the Digital readout was blank. I pushed the UP button and
the furnace did not turn on. I popped it off the wall and found two AAA
batteries. Of course this is 3am and there are no stores open closer
than a 25 mile drive (I live in a rural area).

Then I remembred that my small LED flashlite has AAA batteries, so I
used those. The thermostat had alkaline batts, but the ones in the
flashlite were carbon-zinc, but they worked fine and I had heat again.

That thermostat was installed in here about 4 years ago, when I had some
furnace work done. I never knew it even had batteries, thinking it was
powered from the transformer on the furnace. It's NOT a programmable
t-stat, so aside from the digital readout, it's nothing more than a
plain thermostat.

I never knew those thermostats would completely fail to start the
furnace when the batteries went dead. Apparently so.

Now that I know it has batteries, I will replace them yearly, but I'm
actually thinking about replacing that t-stat with a standard analog
one. The last thing I need is for the pipes to freeze because the
batteries failed, when I was not at home. (Even new batteries can be
bad). There is no advantage to having a digital readout for me. I hardly
ever change the temperture anyhow.

My question is how does this sort of thermostat switch the furnace on
and off? Is it a semiconductor type of switch or what?

Yea, I did buy some new alkaline batteries today and put those in this
thermostat.

(I still think the best Thermostats made were those old round Honeywell
ones with the mercury switch. They lasted decades and never needed any
repairs. So much for so called "improved technology").

My programmable thermostat has an auxiliary thermoswitch that will
turn on the furnace if the temperature goes below around 50F or so,
even if the battery fails or the thermostat itself fails. It's a
Robertshaw, about 20 or so years old. The thermoswitch is clearly
visible on the baseplate assembly. The thermostat itself is removable
from the baseplate so you don't have to stand at it when setting
the program.

I'd expect most decent battery powered thermostats to have a similiar
feature. Otherwise I could see lawsuits against the manufacterers or
the heating contractors when the battery fails and the pipes freeze
and cause extensive water damage.