Heatnglow TownsendII-LP

Cincodemayer214

I've been working with this heatnglow stove and the issue is it will run for 10-30 mins and then the gas valve will shut down completely. I have replaced the pilot assembly and gas valve with the same issue happening. Tech support told me it was a bad thermocouple. I again replaced the thermocouple and used a test adapter allowing me to test the thermocouple in line with the gas valve. It tests in range initially but as the fireplace is on I slowly lose millivolts until there so low the gas valve shuts down. I have verified the venting, verified the pilot is making good contact with the thermocouple, and tried it various ways (logs in, reposition logs, no logs, glass on an off). Curious if anyone has any ideas on what could be the issue.

EdTheHeaterMan

Some Heat & Glo products are designed for non-vented (vent-free) applications. In those models, the flame input is typically limited — often under 30,000 BTU/hr — because vent-free appliances must meet strict combustion and safety standards.

What model number is your gas log?

If you have a vent-free model, it can generally be installed in a vented fireplace behind glass doors, but it is specifically engineered to operate without a chimney draft. In order to be approved as a vent-free gas appliance, it must include a safety device that shuts down the burner if oxygen levels in the room drop below a safe threshold.

That safety device is called an Oxygen Depletion Sensor (ODS).

The ODS system typically consists of a precisely engineered pilot burner and a carefully calibrated orifice. It works in combination with a thermocouple (or thermopile). As the oxygen level in the room decreases, the pilot flame characteristics change — it becomes smaller and lifts slightly off the burner. When the flame can no longer properly heat the thermocouple, the millivolt signal drops, the gas valve closes, and the appliance shuts down.

It does not wait until all breathable oxygen is consumed. The shutdown occurs well before dangerous oxygen deprivation levels are reached. It is a preventive safety measure.

Given the location of your gas log inside the fireplace — particularly if glass doors are closed or airflow is restricted — is it possible that the oxygen level around the burner is dropping during a 30-minute burn? If so, the ODS may simply be doing exactly what it was designed to do.

Cincodemayer214

Thanks for your input but it is not a vent free fireplace. There are no added safety features and has been working in this room with no changes for 30 years.

109A_5

It appears the Townsend II has a Thermocouple and a Thermopile.

Just to be clear, so when it acts up

" it will run for 10-30 mins and then the gas valve will shut down completely "

The pilot flame goes out ?

https://manuals.fire-parts.com/aws-assets/heat-n-glo-townsend-ii-townsend_ii-pdf.pdf?inline=true

Cincodemayer214

Yes pilot goes out. The thermopile tests in proper range but the thermocouple slowly loses millivolts as the burner is on until it drops the gas valve out.