What makes one thermocouple better than another?

JohnNY

A boiler company rep told me recently that Honeywell thermocouples are "about a 7 out of 10" in terms of quality. I'm more inclined to believe Honeywell makes the top-tier stuff but I don't know.
Anyone?

RayWohlfarth

I prefer the Johnson Husky ones myself. They seem to last longer

Steve Minnich

Agreed. I always kept one box of 36” Honeywells and one, single Husky on my truck.

JohnNY

I think the rep's point was there are certain alloys the work better than others. I feel like this is a rookie question but in this season of heavy service I'm tired of getting callbacks for brand new thermocouples that have failed. It happens about half a dozen times per season.

STEAM DOCTOR

There might be some sort of underlying cause. Like carbonized boiler or partially blocked chimney

Larry Weingarten

Hello, I've had pretty good luck with Robertshaw.

Yours, Larry

Bob Harper

Keep in mind the type of thermocouple and its mounting bracket affect the dropout rate. A non-OEM TC could lead to someone attempting reignition while it is still hissing gas resulting in making headlines. More of a problem with hearth appliances but just sayin'. Sure most any 30 mv TC with the correct threads will work but is it the right move?

tim smith

We pretty much always use Baso Husky, 36" and sometimes 72". Always had better mv production and hold up better. Although some pilots won't accept them so we go to Honeywell then.

jfilliez

Been in the business for over 60 years. Have been a Free Lance Hydronic instructor for about 20 of those years. Still at it even though I retired from my business about 5 or 6 years ago.
Been a long time fan of your site and have many of your books for reference.
Keep up the good work.
Jim Filliez

Tim McElwain

About 20 years ago I was part of a test of 100 customers systems using thermocouples. The Honeywell Q340 and the Johnson (now Baso Gas Controls LLC) Husky proved to be equally the best. Some lasted 15 years without needing changed. Some others (not named) maybe 10 years and some others failed with 1 to 2 years.

I also at one time had a restaurant service business and did a lot of pizza ovens. The Johnson K16LRA nickle plated corrosion resistant thermocouple lasted 3 years in those 24 hour a day ovens. All other lasted less than a year and some only 3 months.

A big part of thermocouple failure is environment and also OEM application.

JohnNY

Thanks, @Tim McElwain_4
Great answer.