My thermal cut-off switch for my oil furnace blew and my neighbor replaced it until a tech could come out and check it when I had my cleaning. The switch blew again and the furnace tech bypassed the switch instead of installing a new one. Should a new one be reinstalled, or is it fine to just bypass it? My neighbor said its a safety issue because if it gets to hot the switch won't be able to shut the furnace off.


I would really want to know why the switch failed twice, and running the unit without all safety devices seems like a bad plan. I'd find a new tech (don't use the other guy again) to diagnose the actual problem and install a new switch correctly.

The tech may have never seen a thermal cut-off switch do anything and decided it wasn't needed, but that's not really something that should be done. Your neighbor is right - get it fixed properly.

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  • That's what we think as well, the furnace was really dirty and the he hvac guy was surprised it didn't backfire and smoke us out, it's running great now, I put a call into the town inspector to ask him about it, to top it off a pipe burst up in the crawl space, and my neighbor once again saved us and also wanted to check what the guy did and that's when he noticed what he did – Pam Feb 16 '16 at 15:41
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    The tech could have had good intentions - "That dumb switch isn't really needed and it will cost 3 hrs and $200 to fix, so I'll help the customer out and just remove it." But it is a safety device, and that just shouldn't be done. Back in the days of screw-in fuses, people could stick a penny behind a blown fuse, and it would probably work forever without a problem, but it's not safe, and when there is a problem its a "burn the whole house down" type of problem. – JPhi1618 Feb 16 '16 at 15:47
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    Not to mention if there is a "burn the whole house down" type of problem, homeowner insurance could discover that the safety cutoff was intentionally bypassed and deny any claims. – wwarriner Feb 17 '16 at 1:05
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    Thanks @starrise, that's a very important point I hadn't considered. That would be very bad. – JPhi1618 Feb 17 '16 at 1:07
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    And of course, though it goes frequently unstated with safety issues, OP's life is at stake, along with the lives of their family, pets, and any visitors they may have. – wwarriner Feb 17 '16 at 1:12


The switch is an extremely important safety feature. If you have an oil-fired boiler, it can explode with a tremendous force, enough to destroy your entire house and kill everyone inside. https://www.google.com/search?q=boiler+explosion&ie=utf-8&oe=utf-8#q=boiler+explosion&safe=off&tbm=vid

If you have an oil-fired air heater (no water to explode), in the worst case only your house will burn down.

The fact that the switch already blew twice shows that the furnace has a serious defect, the switch might be the only thing keeping you from disaster.

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    I believe this post was truncated. It should probably end with nope nope nope nope nope nope nope... – Mazura Feb 17 '16 at 3:06

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