My wall heater is not functioning. The pilot light is normal, but the thermostat does not always successfully trigger the heater. After some testing, it seems like I need a replacement valve.

However, my model is pretty old... can't even find model number on the device.
Wondering if people can help figuring out where / which gas valve should I buy?

Thanks in advance!

Photos of the gas heater and valve:
https://photos.app.goo.gl/1S3YPcgBnQiJACa03][/url]

 

Welcome to the forums.

That wall heater is certainly no spring chicken. They only have a limited life before the heat exchanger rusts thru from heat and moisture and allows CO into the room.

Those heaters are very basic in operation. It's possible it's a bad gas valve but not very likely. I added a detailed picture to your pictures. These heaters rely on a large bushy pilot flame to completely engulf and heat the pilot generator. A common problem is the gas pilot orifice needs to be cleaned. I see that pilot generator has been changed recently. Ongoing problem ?

The only way to know what is going on is to measure the two Pg terminals with a voltmeter. You need to measure approx 400-500mv. (1/2 vdc) with the burner not running. Then measure it again when the burner is lit.
Also....while the burner is lit.... measure from Th to Pg (two end terminals).

Pg to Pg +/- 500mvDC - no burner.
Pg to Pg +/- 350mvDC - burner on.
Pg to Th +/- 350mvDC - burner on.

 

Hi Pete,

Thanks for your reply and the attached photo. I just moved into the house a year ago, so I don't really know how old the heater is. Do you think it's not worth the effort fixing it?

And yes! Pilot generator is new! Basically, starting this winter, the heater rarely works. I had to tap the gas valve with a hammer to make it work. Our gas company sent someone to inspect, they tried to clean the gas pilot but they also told me that with this type of model, there is only limited cleaning that can be done.

They also measured (not 100% sure... I believe it is...) Pg to Pg with no burner, and found that it's only like 400 mv. So they suggested me to get a new pilot generator and see if that's the issue. I then replaced it like you have seen in the photo, but the heater still doesn't work...

So, it seems like the only possible problem is with the gas valve itself? What do you think?

Big thanks again!

 

Without making all three voltage measurements..... it's a guess.

 

If the pilot stays on it usually is something else. Thermostat- dirty pity- bad splice. Spider in the burner orifice. The valve you have is a General Controls B-67. Can you hear the valve click when the thermostat is turned up.

 

After taking a second look at the pilot I noticed you have a universal replacement cartridge. Those have a tendency not to burn properly and that may be your problem.

 

Hey mbk3,

Yes. The pilot stays on. I don't hear the valve clicking (but I do hear the thermostats clicking). What is a universal replacement cartridge? Which part are you referring to? I also tried searching for General Controls B-67, it seems like it's already obsolete?

Hey Pete, I don't have a voltmeter with me at this point. I will try to get one and measure the numbers. Thanks!

 

I know it is a long gone valve. I’m sure you can find one on eBay if you don’t want to install another style. The universal cartridge is smaller in diameter so they give you an insert you install the cartridge in. At times the flame doesn’t burn properly on the cartridge. Try leaving the thermostat open and jump the two thermostat terminals at the valve. If the valve opens and the burner comes on come back here and we can continue. A millivolt meter would be a big help.

 

Hey mbk3,
Can I install another style valve inside this same wall furnace unit? I don't mind installing another style valve as long as it fits and works.

How do I jump the valve? And which two terminals is the thermostat terminal? Sorry for these newbie questions and thanks for the help again!

 

Pete made a good comment about the age of your furnace. A heat exchanger inspect is certainly in order before you make any repairs. The thermostat wires are the two coming into the valve not from the generator.

 

If you look at the diagram I labeled..... Th = thermostat.

 

Hey mbk3,
Thanks! Which part is the heat exchanger? Is it the huge portion of the furnace above the pilot? I had our gas company do some safety inspection checkup and they had no issue with it. (not sure if they actually 'inspected heat exchanger').

Hey Pete,
So Th is thermostat, and Pg is?
Also, how do I jump start it? What equipment do I need?

 

Also, by the way, I tried searching for 'General Controls B-67' on ebay, and this is the only thing I can find...
https://www.ebay.com/itm/ITT-General...g/263370932870

 

Don’t buy that valve. Said for parts. The only part is the knob. Call your gas company back and ask them to use their meter. I’m kind of leaning towards a spider in the burner orifice. I’m thinking this may be a bit more than you should handle if a valve needs replacing. There is more to it than just installing a new valve. Wishing you the best

 

Hey mbk3,
I did call the gas company, and I believe they did check the burner. Also, the gas company guy told me that since the burner is ok, and that we got measurement of not enough millivolts into the gas valve, the problem could only be thermopile or gas valve. Then, I changed a new thermopile, but device still not working. That's why I am up here asking for advice on replacing the valve. Do you mean that probably I should get a new furnace unit instead of trying to fix it? Thanks again!

 

I don’t where to go at this point. If you want a more definitive answer you need a millivolt meter. Get one and we will try and help you along. Sound like a good plan? OR you could replace you furnace and have a new one with a warranty.

 

Have you tried giving the valve a whack with a wrench?? No? Do it.

 

Hey mbk3,

Yes. I did whack the valve with a wrench and it works! But not every single time... And after doing this for a few weeks, now it's getting so much harder to make this trick work...

 

There will be no valve whacking here.

Th = thermostat .... Pg = pilot generator

It's a very simple series circuit. So any loss in the thermostat or thermostat wiring is reason for reduced voltage to the gas valve.

 

Thanks Pete for the diagram!

I got the voltage measurements.
With burner (pilot fire) off, it's basically 0 mv everywhere.
With burner on,
PG to PG is ~250mv.
PG to Th is ~150mv.
Th to Th is ~100mv.

Thermostat is always set to a temperature way above room temperature.

 

So that means your thermostat is hogging/losing 100mv.

That's 250mv from the Pg - 100mv from the loss = only 150mv to the gas valve.
Time to change the stat or check and make sure the screws are tight. There should be no loss on the Th line or very minimal.

You can directly short the Th terminals and it will probably fire fine although 250mv is on the low side.

 

Hey Pete,

You also mentioned in your previous post saying that with burner off, I should get 500mv from Pg to Pg, but I am getting 0mv, does that mean something? By changing the thermostat, does it mean changing the thermostat on the wall? Or some wiring between wall thermostat unit to the valve?

By the way, here attached is the inside of the furnace.

 

Try taking the thermostat wires off and measuring resistance (ohms) between the wires with the thermostat turned all-the-way on. There shouldn't be any (or very little) resistance. If there is significant resistance, check the screws, as mentioned above, and check for splices in the thermostat wiring. Replace t-stat wires and t-stat as necessary.

And the heat exchange is pretty easy to remove. They can clog near the top. Take it outside if you need to clean it -- it'll be messy.

If you do need a new valve, try calling MCombs. This one looks pretty close. Don't try to replace it is you aren't confident with your ability to work with gas piping. Pay a plumber and sleep better at night.

https://www.mccombssupply.com/robert...SABEgLv8vD_BwE

 

Burner off but pilot lit. If the pilot is not lit you won't get any voltage.

 

I measured the voltage between the two Th wire instead of the two screws on the valve. It still has 100 mv difference.

Wondering which part of the unit is "heat exchange"? I can't find a way to remove anything else. Also, another dummy question, how do I get burner off (not sure which part is the burner) but pilot on.?

Thanks!

 

With the thermostat turned off or cooler..... the burner won't come on.

 

With burner off, the voltage is 360 mv.

With all those numbers, what do those mean?

Thanks!!!

 

I jumped the two Th wires, and the valve worked!

I then opened up the thermostat, and measured the voltage difference on the thermostat, and got ~100mv as well.
So, the two wires probably are ok, and the problem is with the thermostat itself?

I guess my question now is... how do I know which type of thermostat should I get? Here attached is the photo of my thermostat.

 

Any millivolt thermostat will work.

 

Any basic battery operated thermostat. Honeywell has a few low cost models.

Your image must be in a public forum or privacy turned off to be seen here.
Try posting it directly to the board..... How-to-insert-pictures

 

Sorry for term “whack” after checking thousands of wall furnaces in my career some need a tap after sitting idle all summer.

 

You can buy a new Honeywell gas valve through amazon #VS820A-1088 for about257.00 and a new 750mv. generator for under 50.00 and from W.W.Grainger a new gas valve Item #23UN65 for about 228.00 and a complete pilot and generator for about32.00. Just make sure that the pipe tat sizes are correct and that the pilot flame faces the correct way.

 

Hey Pete, mbk3,

I was trying to short the two Th wires yesterday before my thermostat arrives. Every single time, the heater worked once I short them. However, there was once, where I shorted it like 5 times in a few second, and it still didn't work. Then I realized that I have set the temperature too low, so the burner is not even on.

Would this 'multiple short-ing in a row without burner on' break my gas valve? Because starting from this morning, shorting the two Th does not work anymore... T_T

Also, the pilot flames would then go off after I short the two Th wires...

 

Go out and buy a new 750mv. pilot generator, clean the pilot and the orfice if the pilot flame is yellow or has a lazy flame. All this screwing around will not fix anything. This way you will be sure that you are powering the gas valve with enough voltage to open it if it still works.

 

It looks like a new pilot generator in place and the OP said it was recently replaced. His open circuit voltage sounds a little low. That tells me that the pilot flame is not large enough to heat the pg properly.

 

Yes. I just had my pilot generator replaced.

However, I just learned that my mom did this crazy thing, where she didn't notice that the thermostat (burner) is off. And so she kept the metal (for shorting the Th wires) there for like 20~30 minutes, basically, kept shorting the system while the burner is off...

I guess this might have burned the valve? Or maybe I burned my Pg so I need a new one again? But the voltage difference from my Pg nodes are still 250/350 (with burner on/off), just like before.

But why does the pilot fire go off then if the valve is broken? I would imagine the pilot fire to stay?

 

Keeping a short across the Th terminals is ok. That's what the thermostat technically is suppose to do.

The voltage measured on the Pg terminals should be one thing when just the pilot is lit.... like 400mv and will drop to another voltage when the Th terminals are shorted. This is normal as the gas valve presents a load to the Pg.

This is a 750mv system which means with just the pilot going and no short on the Th terminals you should measure 750mv on the Pg. That would be in a perfect setup. As the pilot flame gets smaller and the Pg is not completely surrounded by the pilot flame..... the voltage goes down. Typically a resting voltage of around 500mv is normal.

 

Hey Pete,

Thanks for the response and the explanation.

Then I guess I have two questions here:
(1) I already installed a new pilot generator, why is the voltage difference only 350mv instead of 500mv? Anything else that might have gone wrong that needs to be replaced or fixed?

(2) Is this also the reason that my pilot fire goes away when I short the Th wires?

Still confused by why the valve suddenly wasn't able to function again... it was working perfectly the first few times when I shorted the Th wires.

 

May it be a cleaning problem?
Any suggestions on where exactly to clean and tools? Thanks again for all the help!

 

There's something funny looking in the last pilot image. It almost looks like an old PG1 pilot generator, with the individual small jets surrounding the generator. PG1's are pretty old and obsolete. With a PG9 you would see the pilot flame coming from the left. Are you sure it's a PG9? I'm not even sure they're interchangeable.