Fuel Pressure Related Reset Problem

NWDan

Hi, our 15 year old Beckett AFG oil burner for residential heating keeps resetting when fuel pressure is too low. We have a .60 gallon per hour nozzle in, but setting the fuel pressure for anything lower than 120 lbs causes it the burner to reset. We'd like to get the pressure lower as the high temp cut off switch engages quite often. Our local oil heating technician doesn't know why it's resetting at lower pressures. Any thoughts?

Jamie Hall

The burner probably is dropping out because of a poor flame pattern at the lower pressures. You may have to do quite a bit of experimenting (you're being a test pilot here) to find a nozzle pattern and pressure combination which works -- or live with the high temperature cutoff. How often is "quite often"?

STEVEusaPA

You can't get much lower than that, maybe a .50 nozzle.
I doubt lowering the pump pressure is going to help your over sized situation.
What is furnace/boiler model#? It's possible you are way under firing the unit. This will lead to poor combustion and poor efficiency.
I don't understand why a tech would drop the nozzle pressure to try to trim the fire, thinking it will result in a substantially drop in btu's.
It's also possible the techs kept lowering nozzle size and pressure and now the wrong end cone is on the burner.
Any nozzle change requires smoke test and combustion test.
If you're going the route @Jamie Hall recommends, it requires the old school method of a 'nozzle substitution test' to find the smallest best nozzle. I don't recommend it. I recommend setting it back to the OEM specs.
If you unit is way oversized for the heat loss of your home (worse in the shoulder seasons), and its the smallest btu unit available, that's as good as it gets with oil.

Jamie Hall

May I add to my comment. I completely agree with @STEVEusaPA . I would go a little further: the nozzle substitution test is very time consuming and expensive, and requires a really good technician. You are experimenting well beyond what the manufacturer of the boiler and the burner intended -- a somewhat dubious occupation for a home owner and a local service person.

EBEBRATT-Ed

I agree with @Jamie Hall & @steveusapa. You need a competent oil technician. You can only reduce the firing rate so much until combustion falls apart. Your substituting one problem for another.

If the boiler is hitting high limit all the time then you need to find that problem and fix it. Occasional high limit trips are ok, not something to strive for

HVACNUT

Agree with all above.
What's the model of boiler?
What head is on the AFG? F0, F3, F6, V1, L1.
Is there a low fire baffle?
I suspect the 'tech' hasn't done much book learin'.

NWDan

Jamie Hall, temp cutoff is set at 200 F. Furnace will heat for about 10 minutes and then reach cut off temp. Then it will cycle a few times until the thermostat temp is reached. And we're not very cold yet here in the Northwest. May be worse later.

NWDan

HVACNUT, I don't know the head name, but it's adjustable. Some I read are not. Maybe is one of the F heads.

NWDan

Thanks Steve. I'll talk with our tech on the suggestions you've made.

HVACNUT

> @NWDan said:
> HVACNUT, I don't know the head name, but it's adjustable. Some I read are not. Maybe is one of the F heads.

Adjustable meaning?

If the retention head is fixed to the end of the air tube, it's an F head and your only going to be able to get a .60 firing rate with decent combustion numbers is with an F0 head. I'm not 100% positive but I don't believe that rate is applicable with the L or V head. My 'Library' is in my service van so I'll check later.

If the retention head is fixed to the nozzle assembly, it's an L or V head. It has the model stamping on the face of the head.

We need to know this info, as well as the boilers make and model so we can help determine if .06 GPH is achievable.

If it's an F head, use your phone to snap and post a pic.
Also pics of the boiler and connected piping. Theres no such thing as too much information. Unless of course it's my wife talking about a friend at work who has a friend, who's brother knows this lady...
Aww man, I missed the homer by Judge.

There are plenty of warm air furnaces with a .50 GPH firing rate, but those are furnaces, not boilers, so there are other important factors involved when dealing with low BTU's in a hydronic boiler.

Jamie Hall

"Jamie Hall, temp cutoff is set at 200 F. Furnace will heat for about 10 minutes and then reach cut off temp. Then it will cycle a few times until the thermostat temp is reached. And we're not very cold yet here in the Northwest. May be worse later. "

That's actually not too terrible. Not great, either, and it's probably not costing you much in fuel -- by itself (although poor combustion may be killing you). However, it is possible that the boiler is oversized, period. It is also quite likely that the boiler badly needs descaling on the water side and a thorough brushing and vacuuming on the fire side. If the space is not heating properly at those temperatures, then you surely need the cleaning, and you might check and see if you have enough water circulation (assuming that is that no one has gotten clever and removed some of the radiation). Then, once you get the boiler nice and clean inside and out, get someone really competent in there with the proper instrumentation to install the smallest nozzle the boiler and burner manufacturers recommend and get it properly adjusted.

HVACNUT

@NWDan

Both the L1 and L2 heads lowest firing rate is .50 GPH, ONLY if it has the correct static plate and air tub length.

NWDan

To be clear though, this is a hot air furnace, not a boiler. Let me consider your posts and I'll get back with you. Very appreciative of your help.

HVACNUT

> @NWDan said:
> To be clear though, this is a hot air furnace, not a boiler. Let me consider your posts and I'll get back with you. Very appreciative of your help.

Man I wish I knew that.
My thumbs hurt.

STEVEusaPA

HVACNUT said:

> @NWDan said:

> To be clear though, this is a hot air furnace, not a boiler. Let me consider your posts and I'll get back with you. Very appreciative of your help.



Man I wish I knew that.

My thumbs hurt.

Yeah now lets turn our attention to dirty air filter, duct work/lack or returns, and TESP.

rick in Alaska

I was wondering how long this would go before someone suggested it wasn't the burner. I was just about to find out what the heating load was, and if the unit could get rid of the heat, and now I know. Yeah, check the distribution system, not the burner.
Rick

HVACNUT

Going back and reading the first post, it is a burner reset problem, and it does say it's a furnace so my bad, but now I have to ask, did anyone test for a cracked heat exchanger?
Is the cad cell eye dirty? That's a sign but a test must be done.
It's 15 years old so that should've been priority one.

GBart

reading this is insanity , 400 doctors for a splinter, he needs a qualified technician to be there in person, almost sounds like it's over sized

STEVEusaPA

HVACNUT said:

Going back and reading the first post, it is a burner reset problem, and it does say it's a furnace so my bad, but now I have to ask, did anyone test for a cracked heat exchanger?

Is the cad cell eye dirty? That's a sign but a test must be done.

It's 15 years old so that should've been priority one.

I'm taking 'reset' to mean bouncing off the high limit often. I don't see anywhere in the original post about it being a furnace. Although we have seen many times a homeowner calling a furnace a boiler and a boiler a furnace.

GBart

if it is a furnace it is probably grossly over sized or the duct work is partially blocked, no return, you name it, we have homeowner sort of explaining what is going on, we do no know what the unit is, what it is rated for, the size of the house, the pics of a beckett burner do nothing, what is the GPH of the unit??? are there zone dampers that are closed??? what??

delta T

15 year old replacement sized to what was there before, duct work undersized, filter partially blocked, blower caked with dirt....sounds more likely than a problem with the burner.....

HVACNUT

> @STEVEusaPA said:

> I'm taking 'reset' to mean bouncing off the high limit often. I don't see anywhere in the original post about it being a furnace. Although we have seen many times a homeowner calling a furnace a boiler and a boiler a furnace.

He needs to clarify.
I think your right, but I take it (now) as, the larger nozzle made the burner open on limit, and then short cycling so he wants to lower the GPH so it wont make limit.

But now that a smaller nozzle is in, and playing with the pump pressure, it keeps going into safety because, well, you know.

Took me a while to catch up, but yes, it seems like a distribution problem. Air filter, blower wheel, wrong fan speed, etc.

Bottom line is what @GBart said, he really needs someone qualified to check the whole furnace and burner.

NWDan

Yes, I'm about ready to have our technician out again, or maybe someone new. Will consider the distribution angle. Filters are kept clean, fairly new motor on fan, ducts last cleaned maybe seven years ago. That sounds a bit long. Two more burner pics below. Amazed at all of your help!

GBart

nice check valve in the return line

GBart

.60 nozzle with the secondary air shutter open and the primary on 4???????????????

DZoro

a lot of air... Let me guess tech doesn't have a combustion analyzer, and a clue. Why does he want to go below 120psi. That is designed to run higher. Anyone cleaned the heat exchanger? Heat exchanger full of soot will cause your problem, and more if it's not cleaned out.

GBart

Would be interesting to see the specifications of the unit not the burner, age, and the sq footage of the home, looking at it seems like it's an old over sized monster that was upgraded to a Beckett, also note scorch/heat marks around burner mounting plate, old oil lines coming up through the floor in the burner compartment??

Jim Hankinson

Looks like a Miller trailer furnace which would explain the oil lines through the floor. Is this installed in a trailer? I used one of these in my work shop years ago running at higher pressure. Worked like a champ.

GBart

That's larger than a Miller and looks like a cement floor.

EBEBRATT-Ed

Scorched around site port. You would be scorched too with that much air. I am sure it has soft ignition

GBart

It may also require the low fire baffle, it may have an F6 head, too who knows.