PB 105 won't stop feeding pellets!

[BoilerMan]

Hi guys, I installed a pb-105 for my uncle two years ago, it has been working well for that time. He called me a few days ago and said it had overheated, as in pegged the gauge at 260F The relief valve blew off and he opened the door to allow the vacuum switch to stop the feeding process.
Well, I went over filled it back up, fired it up from a cold start, and disconnect all the loads to see what it would do when it approached high limit. It heated up to 180 (feed rate 4) and automatically slowed the feed rate to the equivelant of 1, and kept on going in "idle mode" feeding the pellets slowly. All this time it was in Auto mode. Shouldn't it have let the fire extinguish? I let it get to 210F before I connedted the loads back up and pulled the heeat from the unit. The auget light would go on and off, I tried turning the unit to the off position while it was in idle mode, the status light went out and the auger kept on going! I'm about to condem the board as this seems totally wrong.

The overheat light went on and off at random times during this whole thing as well, shouldn't it come on at something like 195? and stay on?

Any help or insite is greatly appreciated!

TS

 

[PassionForFire&Water]

Try this:
Take out the the vacuum switch flexible tube and clean the inside.
Clean also both nipples where the this flex hooks up

 

[wil lanfear]

If the control potentiometer has been used as a means to shut the boiler down since it was installed, its possible that its faulty causing the overheat situation. IMHO, the low temp control potentiometer should not be used to shut down the boiler, they seem to be quite fragile, by design, this is the reason that I installed a little toggle switch wired between the vac switch, one of the blue wires from the vac switch connected to this switch, the other side of the switch back to the vac switch. Using a switch allows me to turn the switch off, pellets will no longer feed, allow the fire to go out, whenever I choose to service the burnpot or a overheat situation.

 

[BoilerMan]

The low pot has not been used at all to shut the burn down. The boiler feeds and shuts down as usual now, but he does not trust it, and neither would I to be honest. I'm going to use a strap-on aquastat on the supply pipe as an emergency dump to the radiant slab, I just don't trust the "board" to know when it's in overheat and energize the blue witre. It is still connected, but the mechanical contacts in the aquastat will also act as a dump control. He does have a new board, I just didn't want to put it in and not solve the problem. Have any of you seen any temp probe failures or have an ohm chart I can check it against? I'm going to put in a switch as you suggest wil, as that's how i shut the boiler down yesterday (pulling a wire off the vacuum switch).

TS

 

[Tdiguy]

I just ran into a similar problem on my own PB105. For me it turned out the spring on the aquastat in the top of the boiler got weak over time and was not making good contact in the well. All i had to do was take the aquastat out move that plastic spacer further up on the wire a bit so i could push the sensor further down and re-install.
To test to see if the aquastat is working set the min temp and max temp down nice and low (lower than what the guage reads the water temp to be) and the status light should turn off indicating that it can read the temps from the aquastat and has no need to fire up. This is also a poor mans way to see what temp the aquastat is reading by adjusting the min and max temps slowly up until the status light goes on because the water temp is below the min. Mind you its not acurate but its much cheaper than calling the dealer.

 

[Tdiguy]

Also check out the mods i have made electrically to my boiler. I have it set up so at 200 the main power to the boiler is shut off, a heat zone is opened up and the circulator starts up.