Blocked Vent Safety or Spill switch

Devlin

I have a hot water boiler Slant Fin Sentry-120 EDP (Electronic Ignition Vent Damper Control).  It uses a "blocked vent safety switch" or "spill switch"- part number 460500000, to control a GVD-6 gas damper.  The spill switch has a reset button and also looks to have high temperature sensing built within - is this true ? The damper itself GVD-6 also has a manual click switch on it to place the damper into the "Automatic Operation" or "Hold Open Damper."   My main question is, if I put the damper into "Hold Open Damper," will the spill switch still shut off the gas if senses too much heat (via, CO2 Gases) ?   Or does this damper need to actually close as an action to also shut off gas ?   Need to better understand how that spill sensor works even if damper is on manual open all the time, and still have the temp sensing for safety gas shut off ? 
I appreciate your tech expertise to help answer my questions. Slant FIn has gone out of business and can no longer offer any assistance to answer questions on their systems.

EdTheHeaterMan

Not fully understanding what CO2 gases have to do with a spill switch. A spill switch operates on temperature only. If the air temperature goes above the setpoint of the switch, the switch will trigger and open the contacts stopping the electricity that powers the gas valve. That air can contain nitrogen. Only, oxygen. Only, it could even be steam. It can contain a combination of nitrogen, oxygen and water vapor. Carbon dioxide plays no role in the operation of a spill switch.

EdTheHeaterMan

In reference to placing a vent damper in the automatic or open always position, there is a switch that is operated by a cam on the damper shift. When the damper is open, the cam on the shaft closes the switch. It is a simple and basic mechanical process. Carbon dioxide does not play a role, and whether that switch is open or closed. Only the position of the damper facilitates an open or closed switch, allowing the gas valve to operate or to be prevented from operating.

pedmec

The spill switch is wired in such a way that it is always operational. in the control world it is wired in series with the gas valve. So if some body does the wrong thing like jump out another safety or you have a chimney issue it will shutdown power to the gas valve. so unless you jump out the spill switch physically you will be protected at all times. Notice that the spill switch is hanging from the bottom of the draft hood? so if you do some stupid with the damper and it is closed it will shutdown the power to the gas valve after the flue gases start to "spill".

EdTheHeaterMan

The Spill switch has no effect on the vent damper. The spill switch does not operate the damper. Your thermostat operates the damper, unless you have more than one zone. Then the thermostat operates the zone control. The zone control end switch operates the damper. Once the damper is operated by the thermostat or zone end switch, the end switch in the damper operates the gas burner control. But the gas burner control will only operate if all the other limits are also in the operate position, the switch contacts on the spill switch, the boiler temperature limit, the roll out switch and any other safety device must also be closed (meaning switch turned on) for the damper end switch to operate the gas burner control.

EdTheHeaterMan

If you want to understand how your boiler operates electrically, This video covers what each electrical part on your boiler does. WARNING, CHANGING THE WIRING OF A HEATING SYSTEM TO BYPASS ANY SAFETY DEVICE MAY CAUSE INJURY, PROPERTY DAMAGE OR DEATH https://www.youtube.com/watch?v=eB8TCjX541M
If you do not have zone valves, then you can skip the sections from 2minute 26 seconds all the way up to 7 minutes 06 seconds, they do not apply to your system. At about 7 min 06 seconds the information applies to your system until the end of the video.

Devlin

I thank you all for your insightful & educational comments.   I actually had a  plumber saying to put jumper wire on the spill switch, cause he thought it was bad based on my system not starting the boiler.   Long story short, he didn't even check the circuit with a meter.....just disconnected/reconnected various system wires, banged here & there around the gas valve and pull/shaking wiring around areas of boiler, and then system did just start to function properly (I suspect after he left that it most likely was the damper hanging up/sticking/not going to full open position - suspect all the banging loosened it to go full open).   I wanted to better understand the system and I was not about to do anything like he recommened to do, since it didn't sound right to me.  He wanted another visit ($$$) to just change out the spill switch and w/no further checks/verification, such as any voltage meter checks done to fully evaluate if it actually can be bad or being the root cause. .....I will never call that plumber again.   After he left, I seen the auto or manual switch on the damper - so if necessary, you could switch damper to manual and see if over time the spill switch would trip, possibly being a bad spill switch or more serious problem from actually tripping out from heat build (via, clogged venting, etc).  So, I wanted to better understand how these switches interacted directly with/or not with the damper and if I was missing anything.   I got verification from all your good responses.
I thank you all again. 👍

pecmsg

I suggest you purchase a "Low Level" CO detector.
Not the UL approved big box store but one that will alarm at 15PPM.