How do you test these bad boy auto reset hi limit switches?

Hello
See pics below
On the left is a pelpro bay view 250 Deg “open on rise” hi limit snap disk and on the right is a Breckwell Big E hi Limit 300 Deg “open on rise” snap disc
The 3 rd pic shows the switch is closed with no heat applied but when in the stove it opens at a lower temp than the set limit and stove will Not stay running!

Replacing them fixed the problem but how can this be tested to show it is bad???

Pic 1-2 shows Pelpro hi limit on left and Breckwell Big E on Right
Pic 3 - shows snap switch is closed with no heat

 

To test you need a controlled heat source that you can sit the switch on and then see what temp it opens.

Possibly use a very small hot plate with an insulator sheet on the plate with a hole just big enough to allow the contact surface of the snap to protrude.

Set the plate to get the desired temp (Use a contact thermometer or an infrared hand held)

A dollar intensive process to set up.

Cheaper to just toss the questionable snaps and move on me thinks

 

Thanks for your comments!
Money & too much time involved. Also that is not a field test which would be better.

My pet pieve is the Auto Reset! If the switch messes up and resets then it makes the problem of the stove stop feeding pellets very difficult to troubleshoot.
Do you think using a manual high limit with a reset button like many other stoves is a much better design?

 

Yes indeed.

An auto reset is a really bad idea....

Not only does the problem become harder to diagnose, it could lead to a serious safety issue..


When there is an over temp...I WANT TO KNOW IT.

If the issue is just a failing snap switch it can be readily diagnosed and fixed....plus you know which switch tripped.

Many times the high limit snaps are wired in series, and this make a diagnosis real tough after the fact.

Was there a burn back??? an over temp in the convection sytem ??? or ?????

I will not use an auto snap on any high limit systems.

 

No burn back, in both cases, the Breckwell and the Pelpro, the stoves would all of a sudden just stop feeding pellets! Sometimes after an hour or after burning a half bag of pellets! Just no ryme or reason!
The snap discs were old like an old circuit breaker and the spring inside was weak and just let go! But when the stove cooled down, it reset! All other parts in the stove can be tested and were tested to work fine!
Too many stoves use these auto resets for Hi Limits, like Travis, Pelpro, US Stove, and Breckwell!

 

Here is another one to add to the pile.
US Stove 6041 Multi-Fueler Hi Limit Snap Disc made by NGT. It says type 43 L77 The L means open on rise but the trip temp is not on there. So I got the trip temp from the manufacturer. It is 170 degrees F (maybe too low for an 8 year old stove!) and another auto reset! In this case the auger motor works on the test cord with no pellets in the hopper but the stove stops feeding after about 45 mins. The vacuum switch was faulty but I replaced it to get this far so I replaced the hi limit and finally found the auger motor just gives up under load!

 

The manufacturing cost is a big part of the equation.

These parts are likely spec'd out and put out to bid..... Low bid deal ya know.

Replace the snaps with a top grade manual reset that meets the stoves original temp rating...should be good to go..

 

A heat gun with a pinpoint adapter,and an infrared thermometer,along with your DMM,you could check one very fast.Also,have some contact cleaner handy,to cool it back down,for repeated tests.That is how I test capacitors on curcuit boards,less the DMM.

 

Waiting--