In article , TimR wrote:
On Nov 25, 6:05=A0pm, (Doug Miller) wrote:

Uh-huh. Did you ever check the rating plate on the heater?

Well, no, I didn't. There's not one in an obvious location.

Keep checking until you find one.

But do you realistically think this could be the problem?

Yes, I do, as I've explained several times. If you have a 120V heater,
original to a home that's nearly 50 years old, it's entirely possible, maybe
even likely, that the neutral (cold) side of that heater is bonded to the
chassis -- a home that old is likely to have been wired with 2-conductor Romex
*without* a separate grounding conductor.

What do you suppose happens when a grounded 240V circuit is connected to
something like that?

In case it's not instantly clear, I'll explain.

One hot leg of the 240 is connected to the hot side of the heater. The other
hot leg is connected to the cold side -- where there's *supposed* to be a
neutral conductor, not another hot. The grounding conductor of the 240V
circuit is connected to the chassis of the heater. And that makes a dead short
to ground from the second hot leg.

These aren't plug in portable heaters. They are installed baseboard
heat, have been in place since the house was built c. 1960. They all
appear to be the identical make and model.

But, without finding the rating plate, you don't know, do you?

I've put a meter on
several thermostats, ones that work and ones that don't. All have 240
volt power. All the thermostats are rated for 240.

That would argue against this particular one being 120V, I admit, but it's
still possible. Maybe even possible that the same unit can be used as either
120 or 240, by changing the posistion of an internal jumper wire.

Do they even make a 110 V model? I guess it's possible but I've
certainly never seen one.

There are *many* 120V baseboard heaters.

Bottom line is that you need a competent, qualified electrician to look at
this and find out what's wrong -- and that description clearly does not
include either you or the guy you've had working on it. You need to get
somebody out there who knows what he's doing.