Replacing R8991A oil primary (obsolete) with modern primary and have pre/post purge.

STEVEusaPA

Hey Forum, I came across this the other day. Old oil primary bad (Honeywell R8991A primary & ignitor), and replaced it with new primary and new ignitor. Simple, following the first diagram.

What I was wondering is if I can re-wire like my second diagram and get both pre & post purge.
Existing sequence of operation:
When a call for heat from t-stat:
1. T-T on board closes T-T on primary control (thru yellow and blue-3 & 6 on molex connector).
2. Primary constantly powered thru Black wire to L1, T-T closing powers Orange wire.
3. Orange wire goes thru molex on 4 & 7. If limit is closed sends power to 8 on the molex (violet wire) to power burner motor and transformer. And if limit is opened, no power to burner motor/transformer.



What I think I can do to give pre/post purge:
(The entire existing wiring harness goes from molex connector to the box on the burner)
1. Take orange wire from molex #7 and jump it at L1 at the primary, giving it constant power (like an older style fan/limit).
2. Take the violet wire from molex #8 and put it on the Limit terminal on the primary control. My thinking is on a call for heat, if the limit is open, nothing comes back on violet to the primary, and the burner motor/ignitor/oil valve stay de-energized. If limit is closed, burner runs off primary in the traditional sense.
3. Wire burner motor, ignitor, and oil valve from the primary as normally done.




As my brother always says (as one word with a southern draw)...ThinkIt'llWork?

I'm ok with it wired conventionally and it works fine. Just wondering if it can/should be done this way and take advantage of pre/post purge.
Thanks
Steve

Steamhead

From the ladder diagram it looks like the old primary was powered thru the limit controls into L1. What I'd do is leave the limit wiring as is and hook up the existing L1 wire that runs thru the limits, to the Limit terminal on the new primary. Then run a new 120V feed to the L1 terminal on the new one. This way, the various limit controls will start and stop the burner as they always have, and the hot feed to L1 will operate the pre/post purge timers.

Jellis

Or... Just get a primary control with Pre and post purge features?

STEVEusaPA

Thanks Frank, I see it now.

STEVEusaPA

Jellis said:

Or... Just get a primary control with Pre and post purge features?

@Jellis This isn't a standard primary control wiring. The original control isn't wired like a typical new primary. The new control requires a constant hot for post purge and diagnostics, and a wire on the limit to tell it to shut the burner off when any limit opens.

Jellis

What is the make and model of your new primary control?

SuperTech

I did something similar to my peerless WBV-03, ran a constant hot to the primary control. It could be my imagination but the boiler seems to stay really clean with a a brief post purge and pre purge.

Steamhead

SuperTech said:

I did something similar to my peerless WBV-03, ran a constant hot to the primary control. It could be my imagination but the boiler seems to stay really clean with a a brief post purge and pre purge.

That's why we recommend those purges!

STEVEusaPA

SuperTech said:

... It could be my imagination but the boiler seems to stay really clean with a a brief post purge and pre purge.

It’s not your imagination. It does make a difference.

EBEBRATT-Ed

Prepurge & postpurge gives a cleaner start and stop. In the old days we had delayed oil valves with the delay built into the valve. They worked....most of the time

SuperTech

Speaking of post purge.... some guys say post purge is a bad thing because it wastes BTUs by sending them up the chimney.
On an atmospheric vented boiler is a significant amount of heat wasted by a 15-30 second post purge? I love keeping the boiler clean but hate the idea of wasting heat. I can't imagine that a 30 second post purge would cool off the boiler that much more than natural draft. Has this been studied? Why not have a post purge on all oil fired equipment?

Steamhead

I would think that the little heat blown out of the boiler on a 15-second post-purge is less than what would be wasted if the boiler gets dirty inside. Don't have any figures to back it up though........

STEVEusaPA

I think the main benefit for post purge is cooling down the heat exchanger to prevent the excess heat that causes a little nozzle drip after the burner shuts down. That to me helps prevent a dirtier light off, keeping everything cleaner.
However, in a power venter situation, you post purging 4+ minutes, so you are getting off cycle efficiency losses out of the building.

SuperTech

> @STEVEusaPA said:
> I think the main benefit for post purge is cooling down the heat exchanger to prevent the excess heat that causes a little nozzle drip after the burner shuts down. That to me helps prevent a dirtier light off, keeping everything cleaner.
> However, in a power venter situation, you post purging 4+ minutes, so you are getting off cycle efficiency losses out of the building.

Thats why I added post purge to my peerless WBV-03. What I'd really like to do is find a way to add some post purge to EK boilers. 3 out of 4 system 2000 boilers I see all show evidence of nozzle drip after shut down. It doesn't cause any major issues but my OCD about making everything perfect makes me want to change them.

STEVEusaPA

I would think the thermal purge from the Energy Manager after a call would help cool down the heat exchanger, no?
It would be a good question for the EK people here on the wall regarding the dripping you see.

HVACNUT

Also the EK 1 Frontier, and I think the new combi with the Beckett burner come with the Genisys 7505B. With the contractor tool it can be changed to a "P" to set up post purge.
I've never reprogrammed one for an EK though as I've never had a need to.

SuperTech

> @STEVEusaPA said:
> I would think the thermal purge from the Energy Manager after a call would help cool down the heat exchanger, no?
> It would be a good question for the EK people here on the wall regarding the dripping you see.

That was actually what caused me to make my first post on this site. The thermal purge helps cool the exchanger but the combustion chamber will really hold a lot of heat if the draft isn't adequate. A lot of homes I see don't get enough draft for the EK boilers until the chimney heats up. I noticed I never saw it happening on power vent models. I was told to ensure proper draft and make sure to check the cutoff on the oil pumps on those boilers. It's never been a problem, I almost never see any issues with the EK boilers that I service. I really like all the EK boilers.

Roger

Thanks to all for your comments, and @STEVEusaPA , it’s great to hear that we helped play a role with your start on heatinghelp with all your helpful contributions through the years!

It looks like everyone has a good handle on this, here are a few thoughts off the top of my head:

With a property designed and operating system, the burner head and nozzle will always stay at an appropriate temperature from the fan with the burner running. Issues can arise from poor draft when the burner turns off.

One of the worst case scenarios is a negative pressure building/home that draws the heat back over the nozzle and head after the burner shuts off. Connecting outside air helps the burner “breathe” to eliminate after drip. We recommend this on all systems (especially as you never know when the home may have an impactful change like a strong range fan or weatherization); it’s required for all our systems that do not have natural draft.

Good draft continues to draw some air after shutdown, also keeping the head cool - this influences the nozzle temperature much more than boiler temperature on our systems as the boiler cools fairly quickly with thermal purge. With inadequate draft, the opposite is also true, and several things can be done to improve draft - see burner diagnostics on this link for more: https://energykinetics.com/heating-professional-resources/

If there are signs of poor draft like substantial after drip or head coking, fixing the draft problem and adding outside air are the correct solutions. This should resolve the cause, although I know some have used a short burner post purge (maybe 15 seconds). Draft must always be strong enough to allow the blocked vent puff switch to operate as a safety. Pre-purge only needs to be long enough to get the pump up to full operating pressure so anything over 1 second is fine.

Post purging the burner does steal some energy, so we avoid it where possible. This must not be confused with with boiler post purge (thermal purge) which puts more heat to use and can save 20% to 40% of annual fuel use. Having a boiler finish hot (no thermal purge) also means that the boiler heat drives off cycle draft and energy loss, so thermal purge saves energy in several ways.

Of interest, the burner fan moves 4 times as much air as the power vent fan running alone; dilution air vent systems like the 90+ Resolute move even less air through the burner during “post purge”, further improving efficiency. Our dilution air vent systems also have a characteristically clean light off.

Roger

Steamhead

@Roger , you don't say so in your post, but are we correct to assume you are with EK?

Roger

Yes, @Steamhead - I’m president. Sorry I neglected that in my signature!

Steamhead

You can set up your profile so that info comes up each time you post, as I have. It's a big help for when you get so busy you forget things like that.

So when are you coming out with a steam boiler? Burnham's MegaSteam reaches 86% AFUE, and they has a sad when we talk about firing it with a powered gas burner. Think you can beat them?

Roger

Thanks, @Steamhead - I appreciate your comment and suggestion. Sorry, no steam boilers in our near-term focus, though.

SuperTech

Thanks @Roger for your input on this. Now that I think about it I'm pretty sure that I don't see this happen on the boilers that have outdoor combustion air piped in as well. Another good reason to recommend this the owners of EK boilers. I wish other manufacturers showed as much commitment to quality and service as you folks at EK do. Happy new year!

Roger

Thank you for such a fantastic compliment, @SuperTech - I appreciate your support. Happy New Year to you and yours!