OT - Gas furnace glitching

For furnace problems related to safety, reliability and potentially expensive repairs (without any assurance that the problem will definitely be solved - called guesswork), it's best to get diagnostic information directly frm the manufacturer. Try contacting a Trane National Service Manager.. it's his/her responsibility to take care of problems like yours. Dealers don't always have the latest technical information.

On the topic of surges and spikes on the line.. if there are any other motorized or high current appliances (such as a freezer) on the same circuit as the furnace, this can cause line voltage lags and spikes as it cycles on/off.

A furnace with a microprocessor controller should have some (maybe minimal) protection from line voltage problems. If it was certain that voltage spikes were the cause, individual suppressors could be installed across the line-ground (and neutral-ground) connections where the AC voltage enters the furnace. These are small inexpensive devices with 2 leads that can be wired into the furnace's power terminals. These are the same supressors found in most surge supressor power strips.

WB ...............

Microcenter (computer retailer) recently had 300 watt UPS units on sale for $19.95. That's cheaper than replacement batteries, which my old UPS needed. I bought 1, then went back and bought 2 more before the sale ended. They work great, and have excellent built in suppression. Being UPSs, they would keep the uP control from losing its settings during short power failures too.

So if the problem really is glitches on the line, I'd recommend something like this. My furnace controls already have a switch and receptacle feeding the control transformer (required by Code for crawl space furnaces), so it would be the work of but moments to add one of these UPSs.

Gary

Also one line to line for differential surge. The two you describe only clamp common mode surge.

Except that good surge suppressor power strips also have inductor capacitor low pass filters as well as the MOVs.

Gary

You can get EMI suppressor or filter modules on the surplus market, they're rated by amperage or wattage. I used to get them from the local electronic surplus dealer, they've folded up shop, though. The one I have is in a flat, square tin can, two isolated teminals in, two out, can is the common ground. Ran about $6 and was easy to get wired up in line with the mini-lathe motor controller. Hash from that was driving my computer UPS nuts.

In Canada, I have no idea who would be a supplier. In the US, Digi-Key and Mouser would be starting places for new ones, Gateway Electronics and All Electronics are two web suppliers that might have them periodically as surplus. Some types are from PC power supplies and have the common appliance cord receptacle, others are strictly a permanent wire-in solution. These eliminate EMI from other sources but don't deal with dips in line voltage or brown-out conditions. For those conditions, a ferro-resonant transformer would be needed, Sola is one brand that shows up on the surplus market.

Having had to replace a controller board on my furnace, I can emphathize. Lots of money for not a whole lot of technology on it.

Stan

Since it gets stuck in the same state each time, could be a "self induced" power spike rather than an external one. For example, the spikes resulting when the control board actuates the draft motor, the gas solenoid or the fan motor. The draft motor comes to mind first as its "off" spike happens when the furnace cycles off - with the fan still running until it cools down.

Are there any accessories wired into the system, like an electronic air cleaner or humidifier? Might try disconnecting those before messing with the furnace.

There are a bunch of sensors in that style furnace - flame sensor, over-temp sensor, draft sensor, I don't know what else. Takes only one to make it stop working, but your description of the problem indeed does not sound like a sensor related problem.

If you have A/C (or a heat pump), dirty evaporator coils can reduce air flow to where the furnace shuts off on the over-temp. Dirty or wet combustion supply air can clog or corrode the burners to where not all will light and it shuts off on account of the flame sensor. These are examples of things you can fix yourself with a suitable shape brush.

Bob

Thanks everyone for your replies to my query.

I've emailed Trane but have as of yet not received a reply so, I have gone ahead anyway and installed a Trip-Lite surge suppressor (3500 Joules) and now have a plug-in furnace. Due mainly to the exhorbitant cost of a new processor board (not much technology or componentry for the price indeed), I felt a surge suppressor was required in any case, no matter what else may be wrong with the thing.

The Trip-Lite also has coax and phone line suppression just in case I want to connect my furnace to the internet :)

In regards to the suggestion for a UPS, I do have a spare 300 Watt unit but decided against trying it as it does not have sine wave output and I question whether 300 Watts is enough to power the blower motor plus all the other stuff.

I considered wiring the Trip-Lite directly into the breaker box to eliminate a junction point but am probably challenging the electrical code enough as is, what with a plug-in furnace, so decided not to.

Now, to wait and see what happens.............

Laurie Forbes

Thanks everyone for your replies to my query.

I've emailed Trane but have as of yet not received a reply so, I have gone ahead anyway and installed a Trip-Lite surge suppressor (3500 Joules) and now have a plug-in furnace. Due mainly to the exhorbitant cost of a new processor board (not much technology or componentry for the price indeed), I felt a surge suppressor was required in any case, no matter what else may be wrong with the thing.

The Trip-Lite also has coax and phone line suppression just in case I want to connect my furnace to the internet :)

In regards to the suggestion for a UPS, I do have a spare 300 Watt unit but decided against trying it as it does not have sine wave output and I question whether 300 Watts is enough to power the blower motor plus all the other stuff.

I considered wiring the Trip-Lite directly into the breaker box to eliminate a junction point but am probably challenging the electrical code enough as is, what with a plug-in furnace, so decided not to.

Now, to wait and see what happens.............

Laurie Forbes

It wouldn't be able to run the blower etc. I was suggesting hooking it up to feed the control transformer, and control, only. But if it is a square wave inverter, I wouldn't use it for that either.

Gary

Are there UPSs in the 2 or 3 hundred Watt range available with sine wave output??

Laurie Forbes

If it plugs in - likely - just put in a strip - the power strips that are protected - and maybe a breaker for safety. Other than that, it is make it yourself type.

Martin

As an afterthought... Even though you "checked the grounds", you may want to go over them again. Remove the ground connections, clean the metal and all areas that need to be grounded, then re-attach and make sure they are secure. Grounding on this type of equipment can be critical and even though they may seem snug, cleaning and re-doing them may solve your problem. Ken.

Yeah.

Gary

most furnaces _do_ have a plug, maybe you should check your local code, hardwiring would be an unusual requirement. more likely the code calls for a certain grade/type connector/jack and the electrician saved time/money by hard wiring.

wrt to the spike arrestors, they probably won't help much. a ferrups xmfr would be my choice. use both if you want. --Loren

Yes, there are but you really don't need one for this application. I'd first see if Trane has a fix for the microprocessor problem as they probably forgot the "lost in space" rebooter circuit when they built them and are now finding they blew it.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried!

I've emailed them but have not yet received a reply - we'll see I guess.

There's a certain irony to this - one buys a high efficiency furnace to save on heating bills and then may have to spend 500 bucks three years later on a $50 circuit board. My old furnace would never have had such a problem.

Laurie Forbes