Heating, Air Conditioning, Fridge, HVAC/cozy n.gas gravity wall furnace
Expert: john t. borgman - 12/27/2012
Question I have a Cozy w355f model furnace about 3 years old. Only occasionally will it follow the thermostat for the first cycle. I have replaced the thermopile and get about 550millivolts at the gas valve and the thermo contacts. I have also tried 3 different thermostats. When it does not respond to a new(higher) temp setting on the TH, if I bump the valve or almost any where on the furnace it lights, runs until new temp is reached and shuts down. Will not restart until physically prompted. I suspected wiring and ran a new 18ga wire about 16ft from the furnace. Same result. I cleaned wire tips and contacts with steel wool Same result. Voltage is consistently 550mv or slightly higher. Oddly enough in early fall when the weather was warmer the system worked perfect, but when the outside and the inside temp. cooled down it began to act up. Ive also noted that some times when if I simply loosen the wires at the TH it will respond if I raise the TH setting but after achieving the new temp it shuts down and will not restart until jumped/bumped or otherwise prompted. Once, I by-passed the in-wall TH wires and wired it with a new set outside the wall TH to furnace, same result
It sounds like one of 2 things. Is there an inline saftey of any kind on that unit? I am not familiar with the brand. My thoughts are if there is a safety that it might be by passed to see if there is any affect.
But probably it is the gas valve itself, assuming that 550 is enough for that valve. Have you cleaned the pilot oriface? The generator should produce up to 750 mv. If the pilot flame is not strong enough it will not reach the maximum output. If that is all good and the warranty on that valve is 5 years, get a tech out and see about replacing it under warranty. You might try one of those little "pencil" torches (about 10 bucks) and put it on the thermopile and get the mv as high as possible and see if that makes a difference. But all in all if you are getting good mv at the valve and even a jumper (eliminating thermostat and wire) does not make it work without "bumping it" you need a new valve.
I just worked on an "old" Williams shorty wall gravity unit today and it responded with a new thermopile as quickly as 350 mv.
The 2nd possibility is remote, but possible. If your inlet gas pressure is too high the valve can actually have trouble opening. I have had a couple over the years that would not open because a hole in the diaphram let the pressure build too high during the off time. That doesn't explain the working in the fall thing unless the gas company has raised pressure due to construction or the diaphram hole is getting worse since then.
Without being there to put on a meter of check inlet outlet pressure and such it is really hard to be sure of this one. Sounds like you are taking logical steps though.
I am in Portland Oregon at Ben's heating 503-233-1779. I work days, so I can only answer early in the day or later in the evening. I only answer public questions for residential equipment. I am very well versed in gas, electric and heat pumps and will only answer residential applications. I have been known the past decade or so, by my employers as the guy you send when no one can figure it out. Trouble shooting is my special. I understand the physics behind air flow, refrigerants and electricity. I understand programmable t-stats, zone controls, economizers, fossil fuel kits and the engineering thought process in the wiring and construction of residential equipment
I was lucky enough to start in this field almost 30 years ago as an installer, for a company that installed the best duct systems I have ever seen, even to this day. The best ,as far as understanding the way air really flows through a duct system, from the return air to the very last supply register . They also had great pride and the duct work was put in, not only to last 50 years, but to look exceptional. Then as I started doing service work, I was again fortunate that I found a 3 year engineering class being put on be a man that was the educational director for the Entire united states for a society called " the Refrigeration Service Engineering Society " And for the next 3 years I schooled at night and practiced what I learned during the day, a great advantage over schooling and then trying to remember it years later.. Versed in duct design manual J heat gain/loss calculations.
Organizations Refrigeration Service Engineer's Society
Publications I have 2 inventions that have gone through the process and been recorded at the National Institute of Standards and Technology from start to finish and thus been invited to national innovation workshops by the dept. of Commerce and the dept. of Energy. They are waste heat recovery devices that N.I.S.T approved as valid and am currently looking for marketing partners to get this product into the hands of consumers and make a BIG difference in Energy savings for every Household and Eatery and take a big bite in the the peak hours power consumption that face our Utilities companies.
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