"The Daring Dufas" wrote:

Is this a wall furnace?

Yes.

Would the model number start with "GWT" instead
of "GW"?

I may have failed to record the letter T - I do make
mistakes now and then - but I'm pretty sure it is as I
listed it. I'll have a chance to double check later today,
or perhaps tomorrow.

If it is what I think it is and the vent safety switch is
not
defective, the vent cap on the roof could be messed up. Of
course it
would help to know if it's a gravity vented wall furnace.

Yes, it appears to be gravity vented. Here is more info I
recorded but failed to post:

Gravity Vented Wall Furnace
ANS Z21.49b-1995 wall furnace
Model# GW-25-6
Serial# P-43-451101
Input btu/hr 25,000
Gas nat

Does that additional info help you?

Thanks.