Best Sequence of operation for boiler/Outdoor reset/Powervent?

Mark_25

I would like to hear some thoughts on best interlock setup for a non-condensing oil boiler with aquastat running on Honeywell outdoor reset controller with a powervent.

There are several ways to interlock everything.

Outdoor Reset calls for heat to powervent which calls the boiler, which seems like it could allow the boiler temp to go lower than the aquastat would normally let it.

Outdoor reset calls for heat, which powers circulators, and boiler remains on separate circuit, calling powervent as needed to satisfy aquastat. Boiler temp remains higher, but at what cost?

How do you wire your jobs when you have this combination?

Andy Morgan_2

Wiring

The powervent circuit should have nothing to do with Outdoor reset. Wire the powervent into the burner circuit, and wire the outdoor reset into either the burner TT or whatever, depending on what O/R you are using. Powervent is not going to control boiler temp. I know that Field shows an alternate diagram thru the aquastat, but to me, it is just more stuff to troubleshoot when something goes wrong. I always wire powervents thru the burner.

Andy Morgan

R. Morgan Mechanical, LLC

J.C.A._3

Reguardless of the boilers ......

Operating steps, the power venter MUST prove draft before the burner will fire.Bottom line.

If a burner can fire before dratft has been proven, it ain't right. Oil fired units can do it a couple different ways,(I personally prefer the 120V circut vs. the cad cell circut as I've seen too many failures this way) but gas fired units should be wired so the draft proving(no matter whose unit is used)will stop the gas valve from getting a call for heat until it has proven. Chris

Andy Morgan_2

JCA What kind

of failures have you seen? I don't seem to be having trouble with wiring them thru the cad cell relays. Maybe I am just lucky so far! Control failures or just lockouts?


Andy Morgan

R. Morgan Mechanical, LLC

Mark_25

I understand the powervent needs to prove draft before the burner should fire, I guess my main question is should I let the aquastat control the burner fire request, or the outdoor reset control it? Seems to me that the outdoor reset could let the boiler temp get much lower than the aquastat would, depending on the amount of heat required in the radiation. It's a VSI/floor radiant system if that makes any difference.

J.C.A._3

Andy,

Had one a few years back where the power venter was wired improperly to the cad cell relay, and became saturated with oil after the power venter proved, and cad cell thought it saw a fire, (parralell vs. series wiring) and the electrician swallowed the bill.

I got a no heat call, and found the boiler saturated with oil, and the power venter still running, along with the unfiring burner.(draft proving switch proved, but 1 wrong wire pooched that!) Pumped about 7-10 gallons of oil into the "boiler room" before the owner came home.

I had to notify the local Fire Dept. that I was lighting the boiler off in the yard of the company that I worked for so they wouldn't come screaming up the street for a smelly fire call. After removing the boiler from the house, putting it in may van and taking it to the parking lot of my former employer, I got it to light. After putting a hose in the feed , and letting it run straight through the return, we succeded in melting the snow/ice filled driveway, and it burned the unburned oil for about 2 hours before we could even see the cast iron in it's splendid glory.

The plumber who installed it came in after the removal made nipples for us to RE-install the boiler with minor movements, to unions, then promptly fired the electrician.

Lessons learned. Always check all safeties before signing a permit form.(luckily MY name wasn't on it!) #2 Trust no one but yourself when filing approval forms. #3 Stuff occurs, make it a lesson, or make it a loss. Chris