Strange readings from Gas Log Fireplace

[whitegold61]

Hey all, I tried searching something specifically around this issue i'm finding with our gas log fireplace, but unable to find anything that matches our case - here's what happens. We moved into this '79 house this year and now it's getting cold we'd like to light our gas log fireplace. Outside the house it looks like the lady had a 100lb propane tank. We're not sure if we're going to use 100lb and it's crazy expensive to get started with that so I hooked up a 20lb tank with a 11 inch WC pressure regulator on it to see how it works.

What happens is pilot looks strong and blue, thermopile is nice and cleaned, burner tube is all cleaned out too. When I switch the burner to ON and the rocker to ON the pilot light dips to half of what it used to be and half of the long burner lights, it has issues getting around the corner.

When the burner is on the pilot now doesn't seem to properly heat the thermocouple. Testing mV i'm reading 450 with just the pilot, but when I switch the burner on and the burner lights, the voltage drops to 0 instantly! I would expect it would gradually go down to 0, but it is 450 to 0 instantly. My thought is that the pilot isn't hot enough to light the pilot when the pressure changes and it closes the gas valve so it doesn't light all the way? But when applying external heat to the thermopile to encompass the pilot with the burner on, the reading never changes from 0 mV.

Bad thermopile? I get good readings with just the pilot, why no readings with the main burner on? Do I not have enough pressure? fireplace says it needs minimum of 11 WC, and 10 WC manifold, which I believe it has. Maybe bad electronics not allowing gas valve to fully open when in burner mode? Any ideas?

Thank you!

Heat-N-GLO GLS-24LP

 

[DAKSY]

Check the gas pressure at the gas valve with a manometer. Your 20 mlb tank may not be giving you what you need.

 

[whitegold61]

Thanks Bob! I don't have a manometer, looks kinda pricy, is there an easier way to find out? It's a 20lb tank with a normal BBQ regulator on it

 

[gthomas785]

If the thermopile voltage drops to 0, it could be bad..
But first what is the BTU rating of your bbq regulator? Either the regulator or the hose could be restricting the gas flow to the fireplace. As long as both those are big enough to supply the whole BTU load then I'd chase the thermopile issue.

 

[whitegold61]

Thanks! I checked the card on the burner and it requires 41,000 BTU, the regulator is listed at 60,000 BTU, so I feel like I have enough since normal regulators have 11 WC and the fireplace needs a min of 11? So maybe thermopile?

I will say I am testing the mV readings from the controller wires, not the ones directly on the unit. Would one of the inputs to the remote drop to 0 when the main burner is on or am I overthinking?

 

[gthomas785]

Thanks! I checked the card on the burner and it requires 41,000 BTU, the regulator is listed at 60,000 BTU, so I feel like I have enough since normal regulators have 11 WC and the fireplace needs a min of 11? So maybe thermopile?

I will say I am testing the mV readings from the controller wires, not the ones directly on the unit. Would one of the inputs to the remote drop to 0 when the main burner is on or am I overthinking?

Sorry you lost me. How are you getting the main burner to turn on - is it connected to a thermostat? For the main burner to light you'd need those thermostat wires to be shorted so it would be normal to have 0 mV across them yeah?

 

[whitegold61]

Sorry, let me attach some pics. I'm testing on these wires that go to a thermostat thing that plugs into a wall outlet. It just has one button in the wall outlet which seems to provide some sort of mV? I'm not using that though for any of these tests. I'm just turning this dial to ON here on the log unit

 

[gthomas785]

Does that rocker switch operate the main burner on and off?

 

[whitegold61]

Yep. When the knob is on ON I can then switch the rocker to ON and the flame lights

 

[gthomas785]

Yep. When the knob is on ON I can then switch the rocker to ON and the flame lights

So I'd guess that switch is in parallel with the control wires so it shorts them together when it's on. That's why the voltage drops down to zero. Still doesn't explain your low gas flow issue

 

[whitegold61]

Gotcha, what would cause a pressure drop when switching the main burner on if I have the right pressure and BTUs coming from the tank?

 

[gthomas785]

It could be several things, there's a restriction somewhere. The fact that the pilot flame shrinks is a clue that it's probably ahead of the valve.

Can you give more details of how you connected the 20lb tank to the fireplace? Any other piping or shutoffs in line? Any chance there's another regulator hiding somewhere?

 

[whitegold61]

Ah, good question. I don't know what setup they had before. Outside just has a tube from the house, so I added a propane tank there with a regulator. Then it goes to the crawlspace where it seems to go to a valve off to the side of the fireplace in the floor where I had to buy a key to turn it all the way open (until it stops). I guess that could explain a lot if it regulated twice thus giving half pressure somehow. I can check in a bit to see if somehow there's an extra regulator.

 

[whitegold61]

Would the key turning valve include a regulator by chance in that unit?

 

[whitegold61]

Here's what is in the crawlspace on the underside of what I turn the key, one side goes outside, other side goes to fireplace unit. Doesn't seem like a regulator? But not sure

 

[gthomas785]

Would the key turning valve include a regulator by chance in that unit?

Not likely, I was just trying to think of possibilities. That valve is just a gas stop and should give a 1/4 turn between open and closed.

Usually, for a 100lb tank you would see the regulator at the tank. But it's possible they had like a 2 psi system and there was a secondary regulator at the gas logs to drop it to 1/2 psi? But you'd probably be able to see it if that were the case.

 

[whitegold61]

This is where it comes out from the crawlspace and here's a changeover it does into the unit. That's about all the difference I can see from the outside