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Plumbing in the Home/Hot water radiators with water but no heat

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Hi, Hope you are having a safe and healthy new year thus far.

 I am in the middle of this project and still meeting challenges.  Had to drain system last year due to cracked radiators and pipes after a freeze and furnace was not on. We finally got pipe fixed and radiators back on line.  Struggling with refill and getting heat to rads.  

 Right now I have 4 radiators hot but only 2 of those filled.  Had the other 2 filled but had to drain for pipe repair other day.  However they are very hot now.  Still bleeding them.  I also have 2 radiators that before they were filled was recieving hot water and getting warm to hot.  At one point had hot pipes on the fill side and return side.  The other day when I turned the furnace back on after another repair these same 2 radiators filled after bleeding. I was over joyed but now here is the problem, They are cold.  The heat is only traveling part way between the radiator and the main line in the basement. As it is very cold now I tried last night to continue filling with return off and furnace heat off.  One of my hot radiators toped off.  But when I brought the heat back up the 2 cold radiators were still full but stayed cold.  
 I still have to fill the upstairs. We are stumped as to how to get the heat to move into these 1st floor radiators and fill the rest.  

 Infor of my system.  Utica gas boiler 1980's circa.  Fit trol expansion tank american air purger on top.  Fill pipe with manual valve before expansion tank and a backflow valve in between. Cast iron radiators with only elbows no valves.  As far as I no zone controls. MY system has one pipe from furnace passing through Air purger conected to what appears to be 1 inch + steal pipe.  Furnace centrally located under house.  The first radiator on the line use to be first floor then ran to 2nd floor  bathroom before it returned.  Then comes one of the radiators on 1st floor that had recieved heat last week but is now full and cold.  The next on the system are two radiators coming foo the same fill cooper pipe.  One is 2nd floor, which recieved water the other day but no heat and has not filled then the 1st floor(which is full and cold)
 The next radiator in line off the main pipe filled last week and has remained filled and is hot.  Then the next off the line is a 2nd floor radiator.  Heat only has barely cleared first floor in pipe but not recently. The next radiator is a first floor radiator directly over the furnace.  It has been hot and has filled for me twice.  Then there is a 2nd floor and 1st floor rad.  I cannot see which one is first due to a wall.  1st floor on gets hot and has filled once this week.  Last radiator off main line has gotten hot consistently but only filled for me once.  

  We tried several recommend method of filling. All bleeders closed starting with first floor.  Bleeding from the closet to the furthest from.  Purging air from faucet above refill.  With furnace on furnace off. System is very quite today. No crackling or banging.  Fill valve is still open, But no progress in getting heat to the 2 cold water fill rads and have not been able to fill all rads on 1st floor or any on 2nd floor when tried.

 Question how do you determine the order the rads come in system.  All of mine feed off same steal pipe in basement with 1/2 copper going to the radiator and back.  One 2nd floor rad also connects to another 2nd floor rad.  Also one of my water filled rads use to connect to a 2nd floor rad but it was taken out of the loop due to multiple leaks. So we did a turn around on the first floor.  

   I hope I was clear but we need help. Cannot afford a heating person.

       Any help will be greatly appreciated.

Catherine

Answer
Catherine, I have read your questions and am still a little foggy as to what is going on. I will attempt to help but I will need some more information and some clarity.

Do you have a circulation pump on your system anywhere?
If you do, is the pump running when you are bleed the air out?
What is the temperature of the water in the boiler when you start to bleed?
What is the pressure reading?
Is your gage operating properly?
When you say you have radiators, I assume you are not talking about baseboard radiation, but cast iron old style radiators...correct?

These and several other factors come into play with a hot water heating system.

Lets start with the basics:
Once you are sure all the repairs and leaks are fixed, begin to fill the boiler. You said the feed valve(water supply) has a by-pass. If this is correct, the by-pass will allow street pressure(like what you get out of you sink faucet) directly into the boiler system. This allows for faster filling and easier bleeding. Watch the gage, when it gets to about 22 to 24 psi, shut the water off. wait a few minutes and check the gage, if it dropping, you have another leak.
No pressure drop? then start at the closet radiator to the boiler on the first floor, drain at least a few cups of water through the  vent and be sure it has stopped spitting air out. Some times a quart or more is necessary. Once that is done, go back to the boiler and bring the pressure back up to where you started. With the system that you described, you will notice a larger pressure drop because the pipes are smaller than normal. 1/2" is to small to feed radiators.
Next, repeat the same sequence on the next closest and then when the first floor is complete do the upstairs radiators.
Two very important  points: The pump MUST be off when you are doing the filling/bleeding and high pressure must be maintained in order to do it completely.

When you get to the last radiator, bleed until it is completely air free then return to the boiler and fire it up.
Now, here is one of the tricks of the trade, before you fire it up disconnect the power to the circulating pump. The idea is to get the boiler and the water in it hot first. This can be done BUT you Must watch the gage temp and pressure. Prior to firing, make sure the pressure is in the 12 to 18 psi range, no more.

OK, if everything is going well, the water temp should be about 130 degrees and the pressure about 15psi. Start the bleeding process stated above again starting at the closest radiator.  

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