Central Gas Heater Isue

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ctwo
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Central Gas Heater Isue

Post by ctwo »

This house has a natural gas heater in the crawl space, probably around late 80's vintage. It fires up and runs for a while, then you may hear:

clicking, one or a few clicks
buzzing, like the clicks, as a single burst or a few, perhaps a solenoid

I think the source is the same, but the duration and character of the sound is not consistent, and it is not a sound that would normally be heard.

What happens is that the fan stays on, but the furnace goes off and will not come back on.

It's done this from day one and the initial suspicion was contractors that remodeled before moving here had replaced the asbestos lined exhaust tubes with new double walled tubes that were too small for the heater (3" vs 4.5" spec'd). That was changed and the problem still presented, but at a much lower frequency - it actually seemed to disappear before the end of the year.

This year the problem is being much worse and I'm not getting enough heat out to bring the temps over 60.

Because of the history, I suspect there is some kind of safety circuit that is preventing the gas solenoid from opening - may blocking it and that is the sound being heard. Of course that is a wild guess. That's all I have.

Any thoughts, ideas?
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John Hasler
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Re: Central Gas Heater Isue

Post by John Hasler »

> Because of the history, I suspect there is some kind of safety circuit that is preventing the gas solenoid from opening - may
> blocking it and that is the sound being heard. Of course that is a wild guess.

Rollout sensor probably needs adjusting or replacement.
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steamin10
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Re: Central Gas Heater Isue

Post by steamin10 »

Not enough info to make a good SWAG.

What brand of furnace? Manual (selenoid controlled,) or computer board? How are you getting a reset to fire up?

There are some furnaces with Honeywell 'smart' valves that fail in odd ways. It sounds like a coil is heating up by resistance and going open or shorting. Gas valves are designed to 'fail safe', that is to close and prevent flow..Other issues are flow switches and limit switches that get weak and open early. If small exhaust tubing caused a venting problem, then the upper limit could be burned at the contacts, so that heating of the bimetal snap switch can cause arcing, and get into your proving circuit.That arc can be picked up in a selenoid as a buzz.

When you fire up and fail again, a good run through of the circuit components with a meter can usually trace the fault fairly quickly. Follow the schematic like a race track and prove continuity, or voltage across the components. Dont forget that thermostats can go bad, even tho thye are simple devices. Electronics are the worst, because people play with them, and get the perameters all crossed up.

Get more info, and see if we can kick this dog to roll over.
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ctwo
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Re: Central Gas Heater Isue

Post by ctwo »

I think this is going to be older than computers. It was 54 when I got home and set it to 62. It's 59 now and it's rumbling away just fine. I'll have to move a bunch of stuff to get down there and then crawl under the house. I'll rally the cheerleaders.

I've not been able to find the book for it. That would at least provide a model number, and it may have had schematics. The system also has sort of electrostatic filters that I've not looked at. Supposedly they just need to be cleaned and there are no paper or fiber filters.

It's starting to click now, so I will just set the temp to 60 where it is and it will shut off until next time I use it.

I'm cheap so I have the timers set the temp to 50 several times each day. That way if I'm cold I will just manually bump up the temp setting and it will reset before bed time, etc.
Standards are so important that everyone must have their own...
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Disclaimer: I'm just a guy with a few machines...
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Steggy
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Re: Central Gas Heater Isue

Post by Steggy »

steamin10 wrote:Manual (selenoid controlled,) or computer board?
If the furnace is from the 1980s it is not likely that it is electronically controlled, that is, with a microcontroller making the decisions. Microcontrollers of that time were generally not certified for use in anything that could fail in a dangerous way, and would not have been used in anything subject to a UL listing.

Most likely, this unit is solenoid and relay controlled, and therefore should be straightforward to troubleshoot. Of course, finding parts may be another matter...
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Re: Central Gas Heater Isue

Post by spro »

I some ways I can relate to this. I have natural gas fired hot water furnace. As Dave said, the gas valve is very sensitive and needs to get a feedback from the temperature of the pilot tube or it cuts off. In your case it may relate to the "cell" or cells you mentioned. These electrostatic cells get very dirty and can be a blockage. The only way I know about them is a small air filter in a room. There is a pre filter and an exhaust filter. The "cell" itself is easily removed to spray clean and let dry. There are constant "snaps" from the unit as it attracts and fries dust particles but they collect on the wires and cannot work anymore, unless cleaned. In my case it is easy with one little machine but consider the feedback to the gas valve through another line saying the filter is blocked.
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