Home Page link

Floor Furnace Main Valve Cycling Problem

Home| Search | About
Login Password
Register Now! Lost Password?

HVAC Discussions - Heating, ventilation and air conditioning. 

Page 1 of 2       1 2 > last >> Bookmark this page:  YahooMyWeb Yahoo!  Google Google  Windows Live Favorites Windows Live  del.icio.us del.icio.us  digg digg  Add to Netscape Netscape
Subject Author Date
Floor Furnace Main Valve Cycling Problem KJS 01-26-2007
If you were  Registered and logged in, you could reply and use other advanced thread options
Posted by KJS on January 26, 2007, 5:16 pm
My home has a natural gas gravity floor furnace from about 1930 which had
been retrofitted at some point with a standing pilot. Two years ago, I
replaced the standing pilot with a cycling pilot control, consisting of:
White-Rodgers 36C84-426 Gas Valve, 3098-134 Mercury Flame Sensor, 5059-23
Pilot Relight/Safety Timer Control, 760-56 Electrode Assembly and F115-0064
Harness Assembly. The Pilot Burner is a Honeywell Q303.

When the thermostat calls for heat, the pilot lights, the spark ceases, and
about 45 seconds later the flame sensor energizes the main gas valve. All
correct, so far.

However, when the burner is cold, the main valve cycles open 1 second/closed
2 seconds perhaps 7-10 times before it stays open. When the burner is hot,
it stays open without cycling, or at least cycles fewer times.

It appears to me that when the flame sensor has been heated just enough to
open the main valve, the inrush of cool air as the burner ignites cools it
back below its shutoff point. I suspect that while the burner cycles a few
times, the flame sensor gets heated further by the pilot so that its
temperature no longer dips far enough to shut the valve.

The pilot must be set high enough so that the flame engulfs the sensor bulb,
but not so high that the flame separates from the pilot orifice or sputters.
Within that range, I can't find a setting that eliminates the main burner
cycling problem. The manifold pressure is set to 3.5" WC, which is what it
was with the previous gas valve. There are no specs on the furnace, so I
maintained the existing pressure and damper settings. The main burner has no
floating, lifting or flashback.

I have had a tech from the gas company inspect the furnace, and also an HVAC
professional. Neither was able to correct the problem. They both did verify
that the installation was correct and that the furnace was functioning
properly (aside from the cycling problem) and vented safely.

Any suggestions would be welcome. (Replacing the furnace is not an option
right now.)


Posted by on January 26, 2007, 6:45 pm

>My home has a natural gas gravity floor furnace from about 1930 which had

>I have had a tech from the gas company inspect the furnace, and also an HVAC
>professional. Neither was able to correct the problem. They both did verify

        Did they laugh much at the 77 year old furnace ?


>that the installation was correct and that the furnace was functioning
>properly (aside from the cycling problem) and vented safely.
>
>Any suggestions would be welcome. (Replacing the furnace is not an option
>right now.)

        Maybe in another 77 years.


--
Click here every day to feed an animal that needs you today !!!
http://www.theanimalrescuesite.com/

Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/

Posted by on January 26, 2007, 10:21 pm

> My home has a natural gas gravity floor furnace from about 1930 which had
> been retrofitted at some point with a standing pilot. Two years ago

"Two years ago", I should have installed a NEW "up to date" furnace to heat
and protect my family.



Posted by Oscar_Lives on January 27, 2007, 12:41 am

> My home has a natural gas gravity floor furnace from about 1930 which had
> been retrofitted at some point with a standing pilot. Two years ago, I
> replaced the standing pilot with a cycling pilot control, consisting of:
> White-Rodgers 36C84-426 Gas Valve, 3098-134 Mercury Flame Sensor, 5059-23
> Pilot Relight/Safety Timer Control, 760-56 Electrode Assembly and
> F115-0064
> Harness Assembly. The Pilot Burner is a Honeywell Q303.
>
> When the thermostat calls for heat, the pilot lights, the spark ceases,
> and
> about 45 seconds later the flame sensor energizes the main gas valve. All
> correct, so far.
>
> However, when the burner is cold, the main valve cycles open 1
> second/closed
> 2 seconds perhaps 7-10 times before it stays open. When the burner is
> hot,
> it stays open without cycling, or at least cycles fewer times.
>
> It appears to me that when the flame sensor has been heated just enough to
> open the main valve, the inrush of cool air as the burner ignites cools it
> back below its shutoff point. I suspect that while the burner cycles a
> few
> times, the flame sensor gets heated further by the pilot so that its
> temperature no longer dips far enough to shut the valve.
>
> The pilot must be set high enough so that the flame engulfs the sensor
> bulb,
> but not so high that the flame separates from the pilot orifice or
> sputters.
> Within that range, I can't find a setting that eliminates the main burner
> cycling problem. The manifold pressure is set to 3.5" WC, which is what
> it
> was with the previous gas valve. There are no specs on the furnace, so I
> maintained the existing pressure and damper settings. The main burner has
> no
> floating, lifting or flashback.
>
> I have had a tech from the gas company inspect the furnace, and also an
> HVAC
> professional. Neither was able to correct the problem. They both did
> verify
> that the installation was correct and that the furnace was functioning
> properly (aside from the cycling problem) and vented safely.
>
> Any suggestions would be welcome. (Replacing the furnace is not an option
> right now.)
>


What a foolish cheapskate idiot!

Replacing the furnace is not an option right now because you would rather
spend shitloads more money and keep it?



Posted by on January 27, 2007, 3:06 pm

>My home has a natural gas gravity floor furnace from about 1930 which had
>been retrofitted at some point with a standing pilot. Two years ago, I
>replaced the standing pilot with a cycling pilot control, consisting of:
>White-Rodgers 36C84-426 Gas Valve, 3098-134 Mercury Flame Sensor, 5059-23
>Pilot Relight/Safety Timer Control, 760-56 Electrode Assembly and F115-0064
>Harness Assembly. The Pilot Burner is a Honeywell Q303.
>
>When the thermostat calls for heat, the pilot lights, the spark ceases, and
>about 45 seconds later the flame sensor energizes the main gas valve. All
>correct, so far.
>
>However, when the burner is cold, the main valve cycles open 1 second/closed
>2 seconds perhaps 7-10 times before it stays open. When the burner is hot,
>it stays open without cycling, or at least cycles fewer times.
>
>It appears to me that when the flame sensor has been heated just enough to
>open the main valve, the inrush of cool air as the burner ignites cools it
>back below its shutoff point. I suspect that while the burner cycles a few
>times, the flame sensor gets heated further by the pilot so that its
>temperature no longer dips far enough to shut the valve.
>
>The pilot must be set high enough so that the flame engulfs the sensor bulb,
>but not so high that the flame separates from the pilot orifice or sputters.
>Within that range, I can't find a setting that eliminates the main burner
>cycling problem. The manifold pressure is set to 3.5" WC, which is what it
>was with the previous gas valve. There are no specs on the furnace, so I
>maintained the existing pressure and damper settings. The main burner has no
>floating, lifting or flashback.
>
>I have had a tech from the gas company inspect the furnace, and also an HVAC
>professional. Neither was able to correct the problem. They both did verify
>that the installation was correct and that the furnace was functioning
>properly (aside from the cycling problem) and vented safely.
>
>Any suggestions would be welcome. (Replacing the furnace is not an option
>right now.)


YMCA?

Page 1 of 2       1 2 > last >>
Similar ThreadsPosted
Gas furnace main shut-off valve December 7, 2006, 2:29 pm
Problem with AC comressor fast cycling February 21, 2007, 9:03 pm
Furnace does not light main burner December 15, 2007, 9:37 pm
pls help: gas furnace short-cycling ... January 23, 2008, 4:23 pm
Cycling too fast?? Furnace or thermostat October 20, 2006, 11:07 am
Carrier 58 furnace pilot gas valve January 24, 2007, 11:23 am
Home furnace: 1 of 4 gas jets seldom lights. Bad valve? December 10, 2007, 12:27 pm
short cycling January 14, 2007, 8:27 pm
When Am I Short Cycling? June 11, 2007, 8:27 pm
Gas boiler - continuously cycling January 13, 2008, 7:48 pm

Contact Us | Privacy Policy

XML SitemapXML Sitemap