Anybody familar with Gas Boilers?

[Nefarious]

We have a real old Gas Boiler system that heats our house using baseboard radiators. It has worked great for 7 years aside from a replacement pilot light thermocouple a few years back.

So this year, we decide to bleed the noisy lines with some help from the trusty Youtube...  

I got a short piece of hose, and a 5 gallon bucket and removed about 1 1/2 buckets of water before it stopped burping air and was a steady light stream of water. So we proceed to cleanup the boiler with a dust and a vacuum. Start the electric pump and its kind making a weird noise, louder and noticeable.

I light the boiler and crank the thermostat to 80F, everything seems ok, temp gauge on boiler starts to rise but pressure does not! Eventually the boiler kicks off and no matter how much I fool with the thermostat will not kick back on.

So, I'm thinking to myself, maybe the system needs to fill back up with water? So I let it sit for 24 hours, get home from work. It lights this time, but still no pressure and eventually kicks off again... Pump is still making strange noise but since it is making noise I am assuming it still works. I took a look at the expansion tank and took a pressure reading on it and it's at 12 PSI, so I don't think that has failed. I am under the assumption that since my boiler is connected to my water line, the lines should fill within at least several hours without the help of the circulation pump. I should add that when I open some of the relief valves, air comes out (hisses) to the noise of the pump downstairs...

Any ideas before I break the Piggy Bank?

[kappa]

what kinda noise is the pump making?  sound like gravel in it perhaps? could be cavitation.. is there a high point vent around the pump?

[Nefarious]

what kinda noise is the pump making?  sound like gravel in it perhaps? could be cavitation.. is there a high point vent around the pump?

Yes, a little bit like gravel. Sounds like air going through it. I dont see any vent around it.

[kappa]

while venting the system, you said you got about 1.5 buckets of water out before clear stream, were you adding water while venting?

is the pump in a low section of the system?

I don't know home heating applications but I understand pumps.. so.. hehe

I would guess perhaps you have drawn a vacuum on the suction side of the pump and the pump does not have enough net positive suction head..

I don't think you have put yourself in a money expenditure situation so not to worry.. pumps just need a few basic things to run is all.. 

[ACE]

I would check and see if the pump has power to it.  Do an Amperage draw aswell if you can.  Im currently taking HVACR in Tech School.  We havent talked much about boilers yet.  

[kappa]

I would check and see if the pump has power to it.  Do an Amperage draw aswell if you can.  Im currently taking HVACR in Tech School.  We havent talked much about boilers yet.  

he said it was running..

[ACE]

he said it was running..

Right.  If you check for an Amperage draw and its pulling high amps something could be wrong with it.  Im just giving suggestions. 

[kappa]

and make sure the electric motor is actually turning the pump.. found this

http://homerepair.about.com/od/heatingcoolingrepair/ss/trblsht_boiler_8.htm

Possible Repairs

    Check the circulator. There is a spring loaded coupling that connects the pump to the motor. When it breaks after the pump jams, the coupling will make a loud noise as the motor runs.



I'm still thinking you have pulled a vacuum on the suction side of the pump.. could be wrong though.. The heat exchanger has to have a vent on it.. The system needs to be solid all the way through except for the expansion tank..

[ACE]

I do see what your saying with the vacuum though. Makes sense.

[morfiend]

 Nef,


  you said it didn't build any pressure!  check the relief valve that it's not stuck open!

  Often calcium build up can cause it to be opened and not allow pressure to build,this is needed to raise the boiling point. The check valve can stop the system from operating on some systems.

  If the pump is making more noise than usual,as Kappa said it could have lost it's prime and again cause the system to not work,these are safety features so you don't explode the boiler!  

  If the system is really old the pipes could be pretty much clogged with deposites and this could be causing the pump issue.  Check the relief valve first though!


    

[kappa]

http://www.gogeisel.com/geiselonline/news/Boiler%20Diagram.gif


if that is how is system is I think I'm wrong as far as npsh goes.. the pump should always have npsh cause of the supply line from city water.. if the city water valve is open of course.

relief valves should burp water, not air I would think.. and a stuck open relief valve would keep you from making pressure but leak water.. should.. hehe

either the pump coupling is broken or the fill valve is closed.. im leaning toward the fill valve.. ha

look on the bright side of things.. the safety aspects of your boiler are working.. hehe


edit:  that diagram also shows a strainer on the return side of the system.. I'd check it clean too.. Hopefully you can valve it out and remove/clean it then replace.

[Nefarious]

The pump is the red object.



This is bell object is what reduces the water pressure down to 12 PSI, the water valve is to the right. It is open.



The big red valve is the return line, this feeds back into the boiler. It is open.



Last is just a close up to its old rusty parts. 

[kappa]

yea, that does NOT look like a cavitation problem.. I don't see how it could be b/c you have the city supply as well as the weight of the water system above it..

does that pressure gauge move at all when the circ pump is cycled on? I'm thinking that will measure pressure on the water side? It should change if even a little bit if the pump is working properly..

is there a rotameter somewhere in the system that measures system flow?

two things i would do is make sure the system is filled and vented and verify the integrity of the pump coupling..

[homersipes]

I dont know much about forced hot water, my system is steam, but I did find this page maybe it'll help ya
http://homerepair.about.com/od/heatingcoolingrepair/ss/trblsht_boiler_2.htm
good luck keep us posted, will do some more looking tomorrow evening after work 

[JimmyD3]

Where did you vent the air at? At the high point for each zone? 

Wouldn't be the first time a pump went out, or debris moved into the pump and caused a jambed impeller. You may need to call a heating specialist.