It is far more than obvious the heater is not operable. Why it is not operable and why it was prevented from working is the issue. Was that reason safety?
You, nor anyone else has to believe the owner: "The owner stated that the wall unit worked last winter, but has been inoperable since the new thermostat was installed." That's an old wheeze heard many times. Three different experienced gas techs working on it, now the fourth not getting it to work is not believable. Nobody removes gas control wires to install a new thermostat.
Unless there is a space issue to fit a replacement, any repairman would know that millivolt gas valves are available at most local plumbing/heating suppliers and Williams heaters and their parts are often sold there; thus experienced repairman can tell when somebody is faking experience.http://americanhvacparts.com/Merchant2/m...ry_Code=gv-wall
If the pilot valve won't stay open when power is applied from the powerpile to the pilot solenoid terminals it is bad. The gas would have to be on for the pilot to work. The failure to pass gas to the pilot would also stop the main gas valve from letting gas past. http://forum.doityourself.com/showthread.php?t=85067
The above wiring "solution" leaves no safety devices in the circuit. A jumper on the thermo side of the valve bypasses any wire resistances to allow the powerpile to energize the valve:
"A jumper on the 'stat side of the gas valve and the heater roared to life" but there is no safety in the unit. Get someone who knows why they are tested for what they do.
There is no need to recall antique wiring when the unit is new enough to be safe and has a wiring diagram on the covers.
There is too much unbelievable in this thread, so people who've been there, done that, are unwilling to cause harm; their licenses are to do the opposite.http://www.heatpro.us/forum/condescend.html
No need to continue this discussion. Call a pro who installs and works on wall heaters.