Heatilator only works with glass front open

[yegodz]

Hi
I have a Heatilator GNDC36L fireplace... I think around 20 years old. Direct vent, top vent with horizontal exhaust through outside wall.

The pilot lights up and burns fine indefinitely. The main flame, however, will only burn reliably with the front glass door ajar (If just loosen the retaining knobs the front glass leans open about an inch).

If I shut the glass door tight, within 30 seconds the flame turns blue and starts lifting and within a couple of minutes it just shuts off - pilot and all.

I have checked the vent for blockage, but I cannot see a problem.

How does the venting actually work? Where does fresh air come in from? It seems like it is a double walled vent. Is it safe to run the fire with the glass front ajar?

 

[DAKSY]

Your vent pipe is a co-axial system.
The outer pipe (6-5/8") diameter which is for the intake
of combustion air. It also keeps the outer portion of
the venting cool, reducing the Clearance to Combustibles (CtC) required.
The air enters the firebox an opening in the lower rear wall...
The inner (probably 4") diameter pipe acts as the exhaust for the combustion byproducts.
You either have a blockage in one of the two systems,
or one (or more) of your sections of venting has become disconnected.
A blockage in the intake side, will cause issues you describe..
Once the O2 in the firebox is consumed, the flames are extinguished.
Bees are the most likely culprit, especially if you turn the pilot off in the spring.
Disconnected or improperly connected venting, can result in combustion gasses
being drawn back onto the incoming airstream. Since the exhaust is O2 depleted,
the Air-to-Fuel (ATF) mixture gets thrown out of whack & the flames extinguish.
Either way, there is EXTREME DANGER burning your fireplace with the front loosened,
It can allow the release of CARBON MONOXIDE into your home.
You absolutely DO NOT WANT to do that.
You NEED to service your unit ASAP to take the proper corrective action.
The first thing I would do is shut the unit down & remove the vent cap,
so you can see what the heck is going on in there.
Let us know what you find...

 

[yegodz]

Your vent pipe is a co-axial system.
The outer pipe (6-5/8") diameter which is for the intake
of combustion air. It also keeps the outer portion of
the venting cool, reducing the Clearance to Combustibles (CtC) required.
The air enters the firebox an opening in the lower rear wall...
The inner (probably 4") diameter pipe acts as the exhaust for the combustion byproducts.
You either have a blockage in one of the two systems,
or one (or more) of your sections of venting has become disconnected.
A blockage in the intake side, will cause issues you describe..
Once the O2 in the firebox is consumed, the flames are extinguished.
Bees are the most likely culprit, especially if you turn the pilot off in the spring.
Disconnected or improperly connected venting, can result in combustion gasses
being drawn back onto the incoming airstream. Since the exhaust is O2 depleted,
the Air-to-Fuel (ATF) mixture gets thrown out of whack & the flames extinguish.
Either way, there is EXTREME DANGER burning your fireplace with the front loosened,
It can allow the release of CARBON MONOXIDE into your home.
You absolutely DO NOT WANT to do that.
You NEED to service your unit ASAP to take the proper corrective action.
The first thing I would do is shut the unit down & remove the vent cap,
so you can see what the heck is going on in there.
Let us know what you find...

Hi DAKSY
Thanks for the detailed explanation - It is as you described... the inner tube is the exhaust and the outer tube opens into a kind of false ceiling of the firebox. The fresh air intake is supposed to flow in the gap between the exhaust and outer pipe, over the 'false ceiling' and down a gap between the rear double wall of the firebox and enter from below.
I took it all apart and put it back together ... no blockages. I notice that there is a severe downdraft every now and then.
Just cannot figure out why the fresh air will not come in.

There are a couple of holes in the bottom tray that separates the valve area from the pilot are which are plugged by high temp silicone sealant. I'm thinking of knocking that out... perhaps some fresh air can enter from there?

 

[DAKSY]

Don't do that. Those holes are sealed for a reason - CO.
Can you post a pic of the cap?

 

[yegodz]

By cap, you mean the cap on the vent as it comes out of the wall on the outside of the house? I'lll try to pull that out today and take a pic

 

[DAKSY]

By cap, you mean the cap on the vent as it comes out of the wall on the outside of the house? I'lll try to pull that out today and take a pic

No need to pull it out, unless you haven't looked closely at it.
If you HAVE inspected it, simply take a pic & post it.

 

[yegodz]

OK, so here are a bunch of pictures....
Looking up the vent from inside the fireplace with the fire box ceiling removed


The firebox false ceiling


The outside vent cap


View of vent with vent cap removed



Link to video showing the flames lifting with and without the glass door closed

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[DAKSY]

Hmmm. Watching your video, it's definitely something in the venting.
That's a REALLY old style cap. Haven't worked with one in YEARS.
It sure seems like you aren't getting combustion air. If you were burning
O2 depleted air, you would be getting some sooting.
I STILL think it's on the intake side. Have you tried blowing compressed air
into the intake? I would try that - with the glass front ON & the pilot off.
Cover the burner with a towel of something to keep any debris from getting
into it...

 

[yegodz]

Thanks... I don't have a source of compressed air. I'm pretty sure the vents are clean.. I can see very clearly into the horizontal section up to the elbow joint and then again look from inside the firebox and see the same elbow joint and all is clear.
Also the hot air exhaust only comes from the inner tube and not from the outer space, so there is no leakage from the inner to the outer tube.
Will probably call in the local heatilator dealer... $150 to try and figure out how to fix this :-(

 

[MarylandGuy]

You would feel so much better about yourself and your heater if you understood it inside and out. Give it a shot yourself and see if you can figure out the problem.

 

[yegodz]

You would feel so much better about yourself and your heater if you understood it inside and out. Give it a shot yourself and see if you can figure out the problem.

Well, I've taken apart the whole thing and I am quite sure there's no blockage. As I said, you can see right through the vents from each side. What I've found is that if I wedge the tray open at the base (the tray that separates the valve from the burner assembly), it runs fine because fresh air can get in from below. Any other ideas?

 

[yegodz]

Hi All,
So finally I had a service guy come over and after 2 hrs of them shaking their heads, they finally discovered the problem. A small section of the inner tube in the exhaust cap had rusted and fallen off. As a result, the hot exhaust that comes out of the inner tube was just getting sucked right back into the intake (the space between the inner and outer tubes). The exhaust air leaking into the intake was causing the fire to be starved of oxygen.
Expensive education, but I guess you learn from experience