High Limit Switch Tripping ? Reasons Why?

[krattigan]

Lately when I have my stove on 3/3 heat/fan on after about 6 hours it goes into shut down mode. Thermo is set to 78 and after room hits 79/ 80 it goes to shutdown. (Stove is in Auto mode...)At this point after a while of shutdown the high limit switch trips and goes into #4 light flashing. Any possible reasons why this is happening. My blower combustion blower is set to max (5) so there should be plenty of air cycle through the stove? This has happened quite a few times in the past week or so.. could my high limit switch be blown? Thanks for your help!

 

[SmokeyTheBear]

Lately when I have my stove on 3/3 heat/fan on after about 6 hours it goes into shut down mode. Thermo is set to 78 and after room hits 79/ 80 it goes to shutdown. (Stove is in Auto mode...)At this point after a while of shutdown the high limit switch trips and goes into #4 light flashing. Any possible reasons why this is happening. My blower combustion blower is set to max (5) so there should be plenty of air cycle through the stove? This has happened quite a few times in the past week or so.. could my high limit switch be blown? Thanks for your help!

And this stove is a what?

When was the last time you deep cleaned the stove and how many bags have you put through it since then?

 

[krattigan]

Stove is a Napoleon NPS 45 just finished putting 1 ton through it (Cubex), brand new this year.... clean it once a weak, haven't cleaned vent pipe. Just started burning Vermont's through it ( straight horizontal vent) THANKS!

 

[SmokeyTheBear]

Stove is a Napoleon NPS 45 just finished putting 1 ton through it (Cubex), brand new this year.... clean it once a weak, haven't cleaned vent pipe. Just started burning Vermont's through it ( straight horizontal vent) THANKS!

I would clean the venting and a several other areas in the exhaust path as well, at 1 ton the combustion blower should be pulled and cleaned along with the cavity it sits in and the areas leading into and out of the cavity cleaned as well.

If your vent is straight out how long is it and does it have at least a 1/4 " per foot rise to it going away from the stove? Basically exactly what is in the vent you have and what diameter is it.

Plugged venting can lead to the exhaust gases having trouble exiting the stove which will cause the heat exchanger to go over temperature. In addition to this being a possible cause, if your stoves fuel feed adjustment isn't correct for the actual pellets you are burning it is possible to overfeed the fuel and cause the stove to go over temperature. It is also possible that the damper if any is set such that the stove isn't allowed to get rid of its hot exhaust gases fast enough and this can cause the stove to go over temperature.

The number one cause of over temperature shut downs is a failing, dirty, or incorrectly set convection fan rate.

While it is possible for the over temperature limit switch to be defective it would be a rare occurrence.

 

[krattigan]

Will try to clean exhaust tomorrow, its about a 3 foot exhaust straight out. no rise. 3inch diameter. I appreciate your time. Good people on this site. Could it make any difference that I noticed this problem after I started burning softwood pellets as opposed to Cubex hardwoods since Saturday (7th)? Would having my convection fan set to high cause a high temp trip....? I am also noticing that the flame is much bigger with past 3heat/3fan settings from my hardwood pellet burn. Possibly lower the heat setting? keep the fan the same?

 

[SmokeyTheBear]

Will try to clean exhaust tomorrow, its about a 3 foot exhaust straight out. no rise. 3inch diameter. I appreciate your time. Good people on this site. Could it make any difference that I noticed this problem after I started burning softwood pellets as opposed to Cubex hardwoods since Saturday (7th)? Would having my convection fan set to high cause a high temp trip....? I am also noticing that the flame is much bigger with past 3heat/3fan settings from my hardwood pellet burn. Possibly lower the heat setting? keep the fan the same?

It isn't normally the heat setting (firing rate setting) but the amount of fuel actually being dumped into the burn pot, a number of stoves have a feed restrictor that gets adjusted to set a certain flame height at maximum firing rate (depends on the stove).

Then there is a procedure to adjust the damper and perhaps the restrictor back and forth to dial the stove in for the pellets it is burning, then the stove's controls take over from there.

So a small dense pellets will deliver more fuel per auger cycle than large puffy ones this will increase the temperatures in the stove's heat exchanger and can lead to over temperature problems. A change in pellets can make up to a 20% difference in the heat the exchanger sees.

But I hope you read what I posted as the number one cause of over temperature problems was.

I have no idea what your manual says about running on high for prolonged times a number of stoves can't be, I don't know about yours.