Top third of radiators heating up only

northernboiler

Hello fellow steamers. Here is my dilema. I have a customers house with 8 radiators and on all of them, only approximately the top third are getting hot. The bottom 2/3's are cold. This condition is occuring on all of the rads.

One pipe steam. Two steam loops. Each loop is approx. 30-35 feet. Each loop has 2 hoffmann 75's. They are all working.
And we verified that they working.
The mains get completely hot within about 10 minutes from initial fire up.
The rads have a mixture of 1A vents (put on by us) and vari-vents (not put on by us). However they all are venting air out of them.
We changed 2 of the main vents with new ones (cannot fit Gorton #2's- not enough head room),
we also changed out a few radiator vents.
No change in the condition.
Water level in boiler is good, no surging.
There is no banging in any of the mains or take offs or in /at the rads themselves.
Rads are all pitched well.

What am I missing here?
Any thoughts or suggestions?

vr608

Most likely the ones with Varivents are venting too fast, which result in the radiators not heating up all the way. I would suggest a slower vent for those, and reducing the venting on the Hoffman's.

northernboiler

We changed all 3 of the vari-vents to 1A's.
set them on #1.
Still no change.
Now to clarify, the complete top 1/3 of the rads are hot.
The bottom 2/3's are not. And they are cold, not warm, cold.
Side to side on each rad.
And it's all 8 radiators on 2 different loops.

BobC

How well does the house heat? If you push the thermostat to get a five degree rise in room temp do the radiators heat better?

Bob

northernboiler

Aaah forgot to mention, we changed the t-stat also.
We installed a T-87 (all we had).
It was an old chronotherm, but we cranked it up to 80.
It really didn't change the condition.
Rads are hot only on the top 1/3.
BTW the pressuretrol is set at .5 with a diff of 1
Siphon loop was clean.
And it is brass.

BobC

Does the boiler develop any pressure when making steam, does it ever cycle on pressure before satisfying the thermostat?

Bob

northernboiler

Yes bob. The boiler does cycle correctly.
However the t-stat never really gets satisified.
The house is just not really heating up.
With only the top 1/3 of each and every rad heating up, it is really taking forever to heat up the rooms.

What is really driving me crazy is this just seemed to happen out of nowhere.
Everything seems to be operating as it should, or correctly.
Now I have seen rads not heat correctly before, we all have.
But all of them, at the same time, and only heating the top 1/3??
This I never even heard of, lest seen this problem happen.
In "theory", it just doesn't make sense.

BobC

It's very strange.

It sounds like you don't have enough steam, have you checked the firing rate to see if it's correct? Is there any chance something happened in the near boiler piping that is reducing the steam getting out to the steam mains?

Bob

Jamie Hall

Actually, in theory it does make a certain amount of sense: there are two real possibilities, but if you say the thermostat isn't satisfied, that leaves one: you are not putting as much heat into the system as the radiators are capable of taking out.

Everything is lovely -- you have the system nice and even, and steam gets to the radiators in a reasonable amount of time... and the radiators manage to condense that steam. How does the boiler output compare with the system total EDR?

Now it is quite true that it can be difficult to get the bottom of one pipe radiators to heat. The vent, after all, is only about a third of the way down, so when steam hits that vent that's it -- no more steam can get in and the pressure starts to rise.

I think some fiddling may be in order -- and the first thing I would try would be, oddly, slower vents on the radiators.

BobC

The 1A's are good vents but you have to be careful to keep the cap centered as you tighten the cap so you get the vent rate you expect.

I'm leaning towards a reduced firing rate for some reason but I could be wrong.

Bob

northernboiler

That thought crossed my mind like 6 or 7 times.
This is a really old steam boiler.
An old Burnham must be around 50+ years old at least
Looks like it has been a conversion to oil.
No rating plates.
That being said, the firing rate of the oil burner has not been altered or it has remained the same for years.
Burner is firing well.
Boiler is clean (flue passes)
The near boiler piping is one that doesn't have an equilization loop.
The headers are direct take-offs to the two different loops.

And an aside, the customer has resisted all of our attemps to convince him to replace this inefficient beast.
He just wont listen. Sometimes it better not to "argue", the definition of insanity.
That said, the mains are heating well, both of them. and the main line vents, vent correctly. The rads just will not heat completely. Only the top 1/3.

I keep running this around in my head, I'm overlooking something.
Other than what I have written.

Fred

Is this a new Boiler? If it is, was it sized properly to the EDR of the radiators? If it's not new, is it firing like it should? Is the gas supply/pressure correct? Does the boiler have a hole in it above the water line and the steam is escaping up the chimney?

northernboiler

OK let me throw this thought out then, anyone think it is possible that the steam cabinet is or has become clogged up?

BobC

When was the last time this system heated everything well and what has changed since that time? Is it possible something shifted that has changed a pipes slope somewhere?

Keep turning over rocks till you find the right rock.

Bob

BobC

I would also put a low pressure gauge on the system to find out exactly what pressure it's running at. Also check the oil pressure on the oil gun.

Bob

Fred

By "Steam Cabinet" I assume you mean boiler? There is nothing there to clog, as it relates to steam. The header and mains are above the water line. Do you have the old thermostat that was on there? You might try to put it back on and see if that changes anything. I'm assumming that since only the top 1/3 of the rads are getting hot that the radiator vents never actually close, right? If that's the case, it can't be air trapped in the rads.

northernboiler

It has been working correctly up until yesterday.
Everything workimg fine.
Plus no banging anywhere in the system.
What I keep thinking is that the boiler is producing enough steam for the mains, but not completely enough for the radiation.
It just feels like I dont have enough volume production.
But the way the rads are heating confuses me.
Could it just be as simple as the boiler itself?
Firing rate excluded,

Fred

You say its a conversion to oil. Is it possible the oil line is partially clogged, restricting the amount of oil getting to the burner? I know you say it is firing well but how did you determine that?
EDIT: When is the last time the oil filter was changed?

Abracadabra

northernboiler said:

It has been working correctly up until yesterday.

How do you know it was working correctly until yesterday?
Don't always believe what a customer tells you. keeping it simple, whatever changed from when it was working to now that it's not working is most likely the problem.

what is the attached edr? Got a picture of the boiler along with near boiler piping? what's the btu rating on the burner?

to me it sounds like a mismatched boiler to the system
or
boiler is losing a ton of water, and cold water is constantly feeding keeping the boiler from creating sufficient steam.

how much steam is pouring out of the chimney?

JUGHNE

Just throwing out another straw to grasp; had a HW Chronotherm t-stat with a shorted heat anticipator element. The boiler would cycle constantly by the t-stat, never the pressure switch. How that might play into things I don't know. Did you try the old t-stat again?

Steamhead

Check to make sure the boiler hasn't developed a hole above the waterline.

nicholas bonham-carter

Overfilling the boiler up to the height of the header, and letting it sit for a few hours will expose any leaks. Look in the firebox, and on the floor for drips.
If so then a radiator survey will be in order to size the replacement boiler.
Are the radiator vents mounted too high, allowing the steam to close them too early?--NBC