Trouble shooting gas fireplace shut down.

[Gerald Larson]

I have a Majestic direct vent natural gas fireplace (G36DVpi) that shuts down after running various short periods of time from five to 30 minutes. I hear a slight click sound when the unit shuts down. The pilot light shuts down as well when the fireplace shuts down, but it stays on continuously when the fireplace is not running.

A service technician recently cleaned the fireplace, installed a new pilot assembly and checked the high temperature limit switch but the problem persists. I would like some advice on troubleshooting.

 

[DAKSY]

Have you taken a reading on the thermopile? If so, what numbers are you getting?

 

[Fingerlakes Fireplace]

I have a Majestic direct vent natural gas fireplace (G36DVpi) that shuts down after running various short periods of time from five to 30 minutes. I hear a slight click sound when the unit shuts down. The pilot light shuts down as well when the fireplace shuts down, but it stays on continuously when the fireplace is not running.

A service technician recently cleaned the fireplace, installed a new pilot assembly and checked the high temperature limit switch but the problem persists. I would like some advice on troubleshooting.

Watch the pilot flame when the fireplace is running. Is the incoming air blowing the flame away from the thermocouple?

 

[Gerald Larson]

Have you taken a reading on the thermopile? If so, what numbers are you getting

Readings yesterday evening:
pilot on and burner off 470
burner on at start up 183
burner on 20 min. 107
burner on 40 min. 113
burner on 60 min. 115 at which point I turned the unit off. Pilot stayed on.


Readings today
pilot on and burner off 455
burned on at start up 140
burner on 20 min. 45 and unit shut down

Restarted
pilot on and burner off 470
burner on 160
burner on 5 min. 110 and unit shut down

Tried to restart
pilot on with reading of 190, but unit would not restart

I usually run the unit with the gas valve at about 75% but yesterday I ran it at full open. When it ran without shutting down I thought perhaps that was the key to keeping it going, although before these shutdown started it ran fine when the valve was not fully open. And now today, with the shutdowns recurring, I am still searching for an explanation.

 

[Gerald Larson]

Watch the pilot flame when the fireplace is running. Is the incoming air blowing the flame away from the thermocouple?

No. The flame stays near the thermocouple.

 

[DAKSY]

Unless you can adjust the pilot flame higher, the new pilot assembly may have included a defective thermopile. Those number should be above 200mV with the burner on.

 

[Fingerlakes Fireplace]

No. The flame stays near the thermocouple

Did you have this problem before the pilot assey replacement?
Does this unit have a vent switch/spill switch?
Does the pilot assey have a thermocouple and thermopile, or just thermopile?

 

[Gerald Larson]

Unless you can adjust the pilot flame higher, the new pilot assembly may have included a defective thermopile. Those number should be above 200mV with the burner on.

The puzzling thing here is the unit will run continuously in the evening, maintaining a reading of around 100, but when in the daytime readings drop to around 60 and it shuts off. The flame in the evening also has more yellow color compared to a blue flame in the daytime. Are these readings a definite indication of a defective thermopile, even as it does maintain about 100 as it runs some, but not all, of the time?

 

[Lennox65]

The puzzling thing here is the unit will run continuously in the evening, maintaining a reading of around 100, but when in the daytime readings drop to around 60 and it shuts off. The flame in the evening also has more yellow color compared to a blue flame in the daytime. Are these readings a definite indication of a defective thermopile, even as it does maintain about 100 as it runs some, but not all, of the time?

If the pilot flame is not engulfing the thermopile in the right position, the millivolt readings will be low. A low pilot flame due to low gas pressure or a clogged orifice may heat the thermopile enough to initially energize the main burner magnet, but will drop off if the flame moves slightly from the thermopile.
Can you take a picture of the pilot flame?

 

[Gerald Larson]

Did you have this problem before the pilot assey replacement?
Does this unit have a vent switch/spill switch?
Does the pilot assey have a thermocouple and thermopile, or just thermopile?

I did have this problem before the new pilot assembly was installed and I don't believe the service tech who installed it tested it to be sure it was working.

The unit does not have a vent switch.
The pilot assembly has a thermopile only.

 

[Gerald Larson]

If the pilot flame is not engulfing the thermopile in the right position, the millivolt readings will be low. A low pilot flame due to low gas pressure or a clogged orifice may heat the thermopile enough to initially energize the main burner magnet, but will drop off if the flame moves slightly from the thermopile.
Can you take a picture of the pilot flame?

The first picture shows a mostly blue flame that leads to a shutdown within 15 minutes or so. The second picture shows a yellow flame that allows the unit to run without shutting down. We get this yellow flame when running the unit in the evening hours.

 

[Lennox65]

If the unit operates differently at different time of day, there must be a connection. Are you using more gas appliances during the day, causing the fireplace to starve for gas from an undersized supply line?

Have you tried running the fireplace with the glass panel removed (just for testing purposes, you can't safely use a direct vent with the glass removed)? There could be a blockage in the vent.

 

[Fingerlakes Fireplace]

I did have this problem before the new pilot assembly was installed and I don't believe the service tech who installed it tested it to be sure it was working.

The unit does not have a vent switch.
The pilot assembly has a thermopile only.

Sounds like a bad gas valve. Your voltage drop from pilot only, to burner on, is too great.
Normally that points to bad thermopile, but since you replaced it, I doubt that is it.
Test the ohms of resistance on the pilot coil.

 

[Gerald Larson]

For the last week or so I have been running the unit with the gas valve between about 50% open to about 75% open and it runs fine, without shutting down. Millivolt readings are between 130 and 160 with the higher readings at the lower gas valve settings.

Today, as I was adjusting the gas valve, I accidently bumped the wire from the thermopile to the gas valve and the unit shut down immediately.

I am perfectly fine with running the unit at these lower settings if this will be a permanent solution to the shutdown problem. But I wonder if the tendency to shut down when the gas valve is fully open and the sensitivity of the thermopile wiring are signs of a problem that will need to be addressed sooner or later.

 

[Lennox65]

If the thermopile wire is connected to the valve correctly, bumping it won't have any effect. There must have been a loose connection.