When a gas furnace gas valve turns off, can it still leak and allow some gas to vent from the burner ports?

[Earl Robertson]

I can smell gas from the furnace after it has been off for several hours. I
have a gas leak detector and I check and am sensing gas at the gas ports
(tubes) long after the gas valve is off. Is this a problem?

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[Ed Pawlowski]

On 12/8/2016 9:14 PM, Earl Robertson wrote:
> I can smell gas from the furnace after it has been off for several
> hours. I
> have a gas leak detector and I check and am sensing gas at the gas ports
> (tubes) long after the gas valve is off. Is this a problem?
>

Yes, it is potentially a problem. If, for some reason the valve is
leaking by it has the potential for fire or explosion. Get a pro to
check it.

[hrho...@att.net]

Get it checked out IMMEDIATELY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[TomR]

In news:d6862$584a1369$a2d350aa$21...@news.flashnewsgroups.com,
Earl Robertson <caedfaa9ed1216d60ef...@example.com> typed:

> I can smell gas from the furnace after it has been off for several
> hours. I have a gas leak detector and I check and am sensing gas at
> the gas ports (tubes) long after the gas valve is off. Is this a
> problem?

Yes, of course it is a problem. If you smell gas hours after you believe
the valve has the gas shut off, you obviously have a gas leak. In my area,
the thing to do in this situation would be to call the gas supply company.
My local supplier is PSE&G, and they come out immediately for any reported
smell of a possible gas leak. It is free. And, they find the source of the
leak and they tell the customer what they find. Usually, they can fix the
problem for a fee, or sometimes for free, depending on where the leak is and
what is causing the leak. They also give the customer the option of fixing
the problem on their own or having someone else fix the problem other than
the gas supply company. Again, no charge if they don't do the work.

You wrote, "long after the gas valve is off", but you didn't mention which
gas valve that is. Did you mean a main gas shutoff valve before the
furnace, or did you mean the gas valve in the furnace? If you meant the gas
valve in the furnace, try shutting off the main gas supply valve before the
furnace and see if the gas smell goes away. If that eliminates the gas
smell, then the gas valve in the furnace is the probably problem and is
somehow leaking some gas when it is supposed to be shut off.

Here is a YouTube video that may also give you some ideas, but it is not
exactly on point regarding your question:
https://www.youtube.com/watch?v=0zKl9wvNIRk

[Ed Pawlowski]

On 12/9/2016 10:24 AM, TomR wrote:

>
> Yes, of course it is a problem. If you smell gas hours after you believe
> the valve has the gas shut off, you obviously have a gas leak.

Or not.

Mercaptan is added to gas so it has a detectable odor. Gas piping can
have an odor for weeks after it is taken out of service. It is possible
he just has residual odor. Since his gas detector is finding something
he should get it checked.

[Art Todesco]

On 12/8/2016 9:14 PM, Earl Robertson wrote:

> I can smell gas from the furnace after it has been off for several
> hours. I
> have a gas leak detector and I check and am sensing gas at the gas ports
> (tubes) long after the gas valve is off. Is this a problem?
>

Sometime back, I had a similar problem. I had replace the thermostat
with a new one which used electronic switching (triac). Apparently
there was enough leakage current through the thermostat triac that
didn't let the gas valve close completely. So there was a very small
amount of gas leaking when the valve was off. I called Honeywell and
told them of the problem. They seemed to be aware of this and
immediately sent me a new thermostat which had relays inside instead of
electronics to do the switching. The "leak" stopped immediately. I
think most electronic thermostats today use relays to actually switch
the gas valve. Actually, in most newer furnaces, the gas valve is not
usually controlled directly be the thermostat, but instead by the
electronic controls in the furnace itself. But even so, my newer
heating system, the thermostat has relays.

[Tekkie®]

TomR posted for all of us...

His new nym will be kaboom...

--
Tekkie

[Bill123]

replying to Earl Robertson, Bill123 wrote:
This is commonly seen by gas utility first responders. If you’re concerned
about current leakage from the thermostat or control you can check for voltage
at the valve. Seems unlikely. Probably the valves aren’t seating properly
because of contaminants in the gas. Just replace the gas valve.
One exception: in very old thermopile systems a weak thermopile output can
cause partial opening without ignition

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[Concerned statement]

My furnace will extinguish the flame after it completes its cycle but with the blower still going about 3 seconds after flame is extinguished it will explode inside the furnace pushing out the door and knocking the filter out of place.. ive determined it has to be the valve not shutting fully and allowing the flame tubes to fill with a little gas and when the gas reaches a superheated spot will reignite.. happens every cycle..

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[Su Nombre]

Concerned statement wrote:

> it will explode inside the furnace pushing out the door and knocking the
> filter out of place..

Sounds like the heat exchanger has a hole in it.