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gas furnace pressure switch bad? Kyle 02-08-2007
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Posted by Kyle on February 8, 2007, 9:09 am


I got a call the other evening from the tenants in our rental house
saying the air was blowing but there was no heat. I checked and they
hadn't mucked up the programmable thermostat, so I figured a service
call was in order.

A technician from the HVAC company we use came out to the house for a
service call yesterday and determined the pressure switch was bad.

I don't dispute the professional's diagnostic, but I would like to
know what the pressure switch on a gas furnace does, since the office
assistant who actually called me couldn't tell me. What kind of
questions should I be asking the company?

And should I ask to talk directly with the technician who made the
service call, since I wasn't able to be there myself for the call?


Posted by Speedy Jim on February 8, 2007, 9:43 am


Kyle wrote:
> I got a call the other evening from the tenants in our rental house
> saying the air was blowing but there was no heat. I checked and they
> hadn't mucked up the programmable thermostat, so I figured a service
> call was in order.
>
> A technician from the HVAC company we use came out to the house for a
> service call yesterday and determined the pressure switch was bad.
>
> I don't dispute the professional's diagnostic, but I would like to
> know what the pressure switch on a gas furnace does,


If it's a newer furnace with a draft inducer fan (90% eff, e.g.)
a small pressure switch monitors the draft conditions and
won't permit gas valve opening unless draft is correct.

Jim

Posted by Tony Hwang on February 8, 2007, 11:00 am


Speedy Jim wrote:
> Kyle wrote:
>
>> I got a call the other evening from the tenants in our rental house
>> saying the air was blowing but there was no heat. I checked and they
>> hadn't mucked up the programmable thermostat, so I figured a service
>> call was in order.
>>
>> A technician from the HVAC company we use came out to the house for a
>> service call yesterday and determined the pressure switch was bad.
>>
>> I don't dispute the professional's diagnostic, but I would like to
>> know what the pressure switch on a gas furnace does,
>
>
>
> If it's a newer furnace with a draft inducer fan (90% eff, e.g.)
> a small pressure switch monitors the draft conditions and
> won't permit gas valve opening unless draft is correct.
>
> Jim
Hi,
Usually the switch is sensing pressure thru a little plastic hose which
some times gets contaminated. Make sure the ais passage is clear.
Switch itself does not go bad easy.

Posted by lp13-30 on February 8, 2007, 12:34 pm


Actually a furnace does not have to be a 90% to have a pressure switch.
All 80's have them too. Pretty much any furnace with a draft inducer has
one. It is actually sensing lack of pressure IOW vacuum to insure that
the inducer is working properly and the unit is venting properly. Tony
is right about the tubes stopping up, usually with condenstation,
however the switches can and do go bad. On the plus side, usually they
are not terribly expensive and are easy to replace. Larry


Posted by Kyle on February 10, 2007, 5:20 pm


On Feb 8, 12:34 pm, LP1...@webtv.net (lp13-30) wrote:
> Actually a furnace does not have to be a 90% to have a pressure switch.
> All 80's have them too. Pretty much any furnace with a draft inducer has
> one. It is actually sensing lack of pressure IOW vacuum to insure that
> the inducer is working properly and the unit is venting properly. Tony
> is right about the tubes stopping up, usually with condenstation,
> however the switches can and do go bad. On the plus side, usually they
> are not terribly expensive and are easy to replace. Larry

Thanks, guys, for the replies. The HVAC man is coming out Monday to
replace the switch. I will be sure to ask him (or have our tenant ask
him) if the air passage is clear or if it needs to be blown out as
well.


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