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My house has several wall-mounted gas heaters.

All but one of them have external, easily accessible thermostats. However, the one that happens to be the most used has no remotely mounted thermostat, to change the temperature you have to open the cover at the base, and adjust a knob at the base of the heater.

Is there any way to retrofit this heater with a simple remote thermostat? Ideally, I'd like something really simple. All the other heaters I have just use contact-closure (e.g. 2 wire, I think) thermostats, not the programmable electronic kinds, and that's all I really want for this heater too.

The heater doesn't currently have any connections for electrical, so an Ideal solution would not require any electrical power. However, I'm not sure if this is possible. I can run power to the heater if I have to, but I'd sure like to avoid any drywall work.

Heater pictures:

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Edit - More Information:

The whole burner assembly is completely separate from the actual heater. It looks like the whole burner, with valve assembly, can be separated from the heater with the removal of just two screws.

Anyways, the heater model is a Williams 35 GV-C-5T NAT (I think. See picture):
enter image description here

The burner assembly and valve is a RobertShaw Grayson 7000 SRLC:
enter image description here

Of note is that on the instruction plates in the heater, there are several diagrams that show a similar valve that supports a remote thermostat:
enter image description here
enter image description here

However, in both cases, the images are for a 7000 M VRLC or M VRCLC, while the heater I have is a S RLC.

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This unit has a pilot light on all the time? No electrical internal ignition? – shirlock homes Jan 13 '13 at 12:16
    
@shirlockhomes - Correct (well, except when I turn the pilot off for the summer, but then I have to manually re-light it in the winter). – Fake Name Jan 13 '13 at 12:24
    
Holy crap, a 7000 MVRLC valve is ~$150! – Fake Name Jan 14 '13 at 7:46
    
How do I distinguish a valve that will work with my wall-unit from one that won't? – Fake Name Jan 14 '13 at 7:48
    
Are all the heaters of the same make/model? What gas valve is in the other units? – ThreePhaseEel Jun 2 at 23:37

I think what you have is a mechanical thermocouple sensor that is connected to the regulator. This is the same as one would have in an RV. They do not use any electricity, and the thermostat is part of the gas regulator. The only remote I am aware of would be a remote thermocouple. I'm not sure if your unit has a removable sensor. If it does, then you can place the sensor elsewhere, but you will still have to set the desired temp on the dial in the unit. There is no actual remote thermostat for this type of unit that I am aware of.

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In that case, could I replace the whole valve assembly? I'm willing to take the whole burner out and replace it, if need be. – Fake Name Jan 13 '13 at 15:43
    
If you can post the make and model it would be much easier to research a conversion valve for ya. – shirlock homes Jan 13 '13 at 15:47
    
One issue to consider when replacing the valve assembly is that upon removing the old one you may lose the direct temperature sensing in the furnace itself wherein you may end up with no over temperature cutout. That could be a big safety concern. – Michael Karas Jan 13 '13 at 16:02
    
@MichaelKaras - I don't think that'll be a problem, as there doesn't seem to be any overtemperature cutout at all. Remember, this is a heater from the 60s/70s. – Fake Name Jan 14 '13 at 7:30

The style of gas valve you have has a separate temperature sensor which cannot be adapted to a remote thermostat. It also uses a "thermocouple" to ensure your safety if the pilot light is extinguished.

You can install the gas valve with a "M" code designation, this one works with a "Powerpile" type of control, it generates its own power for a remote thermostat. But be prepared, these valves are expensive!

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On a Coleman wall furnace with a standing pilot, I used a Honeywell V800A1070. I threw in a 24V step-down transformer wall thermostat and I also didn't have any rollout protection. It runs on one setting until the thermostat is satisfied.

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This isn't impossible, but you'll want someone who has done it before

You will indeed need to have the gas valve replaced to install a thermostat on this heater -- your existing valve (a Robertshaw 7000SRLC also known as a Robertshaw 710-204) is a hydraulically operated thermostatic valve that has no electrical actuation means, just a safety magnet and thermocouple system. According to the Sears Parts Direct page for your heater (the C in the model number appears to be irrelevant), a suitable substitute is a White-Rodgers 36C03U-433. This valve is a millivolt gas control and thus can be used with millivolt-compatible thermostats -- the existing thermocouple will need to be replaced with a thermopile generator to perform this substitution as well.

Other options could include replacing the wall furnace wholesale (a Williams 3509822 is a suitable replacement which supports millivolt control), or using the Robertshaw 7000MVRLC/MVRCLC millivolt valves if the 36C03U-433 is unavailable. I strongly recommend having this job done by someone who is experienced in commercial gas appliances, BTW -- gas valve retrofits like this are vastly more common in commercial/industrial work than they are in a residential setting, and I suspect that many residental plumbers who work with gas aren't going to be very experienced with this type of job.

One final note is that your heater may or may not have a safety switch -- it appears that the Robertshaw 7000 (nee 710) series does not support a high-limit system that operates outside the thermostat system.

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