Furnace Limit Switch

[kenmbz]

I have a love hate relationship with high efficiency furnaces. At my last house, needed to replace internal plumbing for drainage after 5 years. internal fans and a switch.
At new house apartment has higheff and is about 20 years old, and not a single issue, Oil burner in main house, replace transformers every 2 years, replace controller, replace nozzles almost every year. Have that one under contract, luckily. However it is 35 years old and still around 84% efficiency.

So many safety switches on the newer ones and big controller boards, lots of status lights. Most problems easy to fix/troubleshoot. But flow problems are tough.

 

[user.69169]

Furnace still a furnace, firebox, heat exchanger & fan to blow air across exchanger.

Government stuck nose in game and industry happy to complicate to accommodate. Heat exchanger got thinner fer better transfer & shorter use life. Manufacturer and dealer/installer love dat. Add computer to do what real switch did for 50 years and misrepresent product to buyer.

You want real fun, try running recent Becket oil burner on generator during power failure. Old burner control worked fine in dat situation. New computer control wid electronic timer shuts down during start cycle if power comin in is 2hz off 60.
How about fun of "technician" who cleans & services oil boiler widout running wire brush thru heat exchanger. I give you hint, weedwacker cable in battery drill will poke thru built up carbon and clean exchanger. Good soot vac helps too. NO, tossin new nozzle in back corner of boiler housing not same as putting on burner head, but "technician" swears he put new nozzle on boiler.
(removed) getting to point he don't trust Yankee people.

When we on Longggg Island after hurricane watch lot of #2 oil floating on water. Lot of leaking underground tanks oil dealers loved filling. Probably half leaked but dealer didn't mind pumping oil into ground.

 

[ultrarunner]

Very few days in the 30's and few above 90...

Furnaces tend to last a very long time... I have a 90 year old central furnace and no issues.

That said many I know upgrade for efficiency but the tradeoff often is increased frequency of repair.

The less you use the longer to recoup savings from "Upgrade"

 

[user.69169]

Very few days in the 30's and few above 90...

Furnaces tend to last a very long time... I have a 90 year old central furnace and no issues.

That said many I know upgrade for efficiency but the tradeoff often is increased frequency of repair.

The less you use the longer to recoup savings from "Upgrade"

You forgot to mention benefit of Japanese Current.

BT HVAC company here pushes Government program fer new HVAC. Salesmen so good dey replacing 4-5 year old systems dey put in fer tax credit gonna pay.

I love upgrade to argon filled UV shading windows people. Payback period is 27 years in NY. Love even more telling peed off woman watching her house plants dropping dead how she killed dem wid UV resistant windows. Just one time I wanna see one dem wimmen get hands on window salesman.

 

[kenmac]

Repaired a furnace that kept cycling on and off on high limit (the one in the heat exchanger that you can't reset. when the chamber cools down, it resets it's self)
Anyway, I took the blower door off and found some duct insulation had fallen loose and sucked against the blower restricting air flow.

After repairing this return section of the duct. I removed the duct on the supply side to find the same problem.
Duct insulation had come lose and blocking air flow.

Took about 4 hours of taking the duct work apart and re attaching the insulation,
Rechecked operation, and All is good. Furnace (burners) stay on their entire cycle .

Happy customer his house is now nice and toasty. Before, the furnace wouldn't keep the home above 65 deg due to the limit shutting the burners down.

Not gonna say this is your issue because all the high limits I have ever seen reset themselves. They aren't of the type that you push a button to reset

 

[MoKelly]

Repaired a furnace that kept cycling on and off on high limit (the one in the heat exchanger that you can't reset. when the chamber cools down, it resets it's self)
Anyway, I took the blower door off and found some duct insulation had fallen loose and sucked against the blower restricting air flow.

After repairing this return section of the duct. I removed the duct on the supply side to find the same problem.
Duct insulation had come lose and blocking air flow.

Took about 4 hours of taking the duct work apart and re attaching the insulation,
Rechecked operation, and All is good. Furnace (burners) stay on their entire cycle .

Happy customer his house is now nice and toasty. Before, the furnace wouldn't keep the home above 65 deg due to the limit shutting the burners down.

Not gonna say this is your issue because all the high limits I have ever seen reset themselves. They aren't of the type that you push a button to reset

Thanks. I’m sure this high limit switch wasn’t my issue as the furnace didn’t run for approx. 11 hours. The house went from 70 degrees to 61 degrees - we had 3 space heaters going.

I assume if it was an automatic on/off when heat exchanger cools, it would gave come back on in 11 hours.

Knock on wood, we are still going strong.

MoKelly

 

[MoKelly]

Here is an interesting problem I had about 2 years ago.

It happened at a Lake house we owned that was a vacation place v. permanent residence.

I went down one weekend. It was summer. Unlocked the door and it was boiling hot inside. Heat was running. Thermostat was at 99 degrees (it only went 2 digits).

I turned off the system (it was originally set on cool when we left last time) and the heat stopped.

Here is a picture of the candle on the fireplace mantel.



Turns out an animal (guessing chipmunk) chewed thru some wires outside and somehow made the heat run non-stop. Guy replaced the wires and all was well. Never happened again.

MoKelly