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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8299
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have weil mcclain boiler with a unico air handler, the

Customer Question

I have weil mcclain boiler with a unico air handler, the first and second floor handlers call for heat the blower will run intermitenlley and the thermostat will still call for heat without reaching temperture. I've checked for air in the system and found none. the boiler reaches 180 we still have hot water in the storage tank and the circulators all run.
Submitted: 8 months ago.
Category: HVAC
Expert:  Rick replied 8 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

Is the piping coming back to the boiler from the air handler(s) hot (as a pistol)?

Customer: replied 8 months ago.
they are hot
Expert:  Rick replied 8 months ago.

What's the model number of the air handler.

Customer: replied 8 months ago.
Mb2436l
Expert:  Rick replied 8 months ago.

Ok, can you locate the aquastat that's on the hot water piping to the air handler?

Customer: replied 8 months ago.
I see it.
Expert:  Rick replied 8 months ago.

Is it connected to a pump relay? do you have 2 air handlers?

Expert:  Rick replied 8 months ago.

I have been called away. I'm going to open this up to my colleagues so one of them can help. Please don't respond (even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer.

Customer: replied 8 months ago.
I have two air handler, I had an hvac tech out yesterday he said the problem is the boiler side. He not work on boilers.
Expert:  Phil replied 8 months ago.

Hello, in my 56 years fixing boilers, I have bled the air out of the radiators only to find them air locked again... bleed them again, run the pumps for30 minutes then bleed them again.

Let me know how that goes, we can go from there as needed.

Expert:  Phil replied 8 months ago.

Tell me in great detail what valves you open to bleed the radiators...some people use the wrong valves, I need to know which ones you are using and where they are located on the coils and what they look like.

Customer: replied 8 months ago.
There are no radiators. It's a cool to two Unicom air handlers one in the basement for the first floor the other in the attic for the second floor.
Expert:  Phil replied 8 months ago.

Hello again

https://www.unicosystem.com/files/2313/8930/2966/Bulletin_30-020_2010-12.pdf

tell me if this is what you have or not, if it is, see page 2 it shows the heating coils positioned in the air handler, there is an air bleed port at the high point in each coil.

Customer: replied 8 months ago.
I attempted to bleed on the returns on the boiler , not the cool side.
Expert:  Phil replied 8 months ago.

Bleed vent is show on page 13

You mentioned checking for air in the system earlier, that would have been done at the bleed vents (AIR bleed vents)

Bleeding at the returns will not work, air is trapped at the HIGH points in the system only.

Expert:  Phil replied 8 months ago.

Bleed ONLY the hot water coil.... do not bleed the 'cool side' (cooling coil if that is what you meant.

Customer: replied 8 months ago.
I loosened the vents nothing is coming out but the cool is hot.
Expert:  Phil replied 8 months ago.

THe boiler must be under pressure, 20 to 25 psig in order the force the air out of the system when hot.

I need to know in great great detail what you mean by "the cool is hot"

we can go from there

Expert:  Phil replied 8 months ago.

There is a pressure gauge on the boiler that tells you what the boiler water pressure is.

Customer: replied 8 months ago.
The boiler is 20 psi I typed the coil is hot. My Samsung changed it to cool.
Expert:  Phil replied 8 months ago.

Hello, what is the temperature of the air that comes off of the coil?

Expert:  Phil replied 8 months ago.

You forgot to tell me if you found the tiny air bleed screw at the high point on the coil as shown on page 13, figure 16.

Expert:  Phil replied 8 months ago.

Either a squirt of air or water should come out when you turn that screw counter clockwise

Customer: replied 8 months ago.
I got a little water dribbling out and closed it. Could the problem be at the boiler control?
Expert:  Phil replied 8 months ago.

The problem could be anywhere. Tell me how high above the boiler the Unico air handler is please. within 5 or 10 feet is close enough.

Expert:  Phil replied 8 months ago.

Is there a reason that you did not answer my previous question:

Hello, what is the temperature of the air that comes off of the coil?

Customer: replied 8 months ago.
There are two one in the basement is about three feet up the one in the attic about 20 feet above.
Customer: replied 8 months ago.
I haven't measured the temperature there .
Expert:  Phil replied 8 months ago.

Thanks, ***** ***** bleed both coils, repeatedly, you should get a significant squirt of water out if the boiler pressure is 20 psig.

I need you to measure the air temperature that comes off of each coil. Auto supply stores carry probe type dial thermometers for about $6 each, buy several they are used a lot in this business.

Customer: replied 8 months ago.
I measured the temp at vent after manually turning the fan on. It read 117 and a second one read 109.
Expert:  Phil replied 8 months ago.

the crucial thing to know about ALL hot water boiler systems is air accumulates at ALL high points in the system, even an inverted U shape, it trap at the top of the U and stop water flow

Customer: replied 8 months ago.
all the lines were installed with breeders in the feeds and returns. The system was installed 15 years ago and has worked fine .
Expert:  Phil replied 8 months ago.

I need the air temperature as massive amounts of air flow past the coil.. not at the vent.

Earlier you said the pipes connected to the coil were hot, but now it seems only 109F water comes out the vent... its one or the other, cannot be both.

again I need the temperature of the AIR as it is blown across the coil on the down stream side.

Customer: replied 8 months ago.
it was the air vent on the floor that I measured temp on not the bleeder vent on the coil.
Expert:  Phil replied 8 months ago.

You need a few hours of basic training on how boiler systems work in order to follow my directions.... there IS NO air vent on the floor... only drain valves.

Tell me if you want 10 hours worth of training or not, we can go from there.