Refilling central heating system

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  #1  
Old 06-13-05, 01:07 PM
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wotbus
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Refilling central heating system

I recently drained my CH system in order to remove a downstairs hall radiator [for decorating and fitting a thermostatic radiator control]. Thinking refilling would be relatively simple, I did the following: closed all the bleed valves on all radiators and opened radiator controls to full, and lastly opened the water feed tap. I then went to all the radiators in turn from the ground floor up to the 2nd floor, bleeding radiators as I went. All appeared to go ok and the new repainted radiator checked for leaks and found all ok. Some time after though, I found a leak from the boiler water pressure relief valve, situated on the ground floor, so I rapidly had to drain the system again. I used this way of refilling a couple of years ago but not with this problem. My question is this: is there a recognised way of refilling a system as I would seem to have created some sort of air lock which is forcing water out of the boiler pressure relief valve. This valve by the way, has a little cover which can be screwed right down to seal ! - almost as though you may have to do this in the first instance in order to "prime" the boiler whilst refilling? then opened afterwards to ambient air pressure. Any advice would be appreciated
 
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Old 06-13-05, 04:42 PM
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pressure relief

The leaking device is not the pressure relief. It is an automatic air vent, which is practically useless on a radiator system anyway. Just screw the cap down to stop the leak & don't worry about it. This is a very common occurance.
 
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Old 06-14-05, 12:42 AM
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wotbus
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Well, nice one Grady. Thanks for the tip.
 
  #4  
Old 06-14-05, 12:56 PM
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Yo, Grady. Very happy to report the system is up and running just as it should - no problems. She's shut down again now ready for the winter but with peace of mind. Thank you for your advice, and best regards.
 
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Old 06-14-05, 04:37 PM
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My Pleasure

Glad I could help.
 
  #6  
Old 07-04-05, 07:37 PM
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Timely thread and nice response Grady.

I have a hot water system with gas-fired Burnham boiler, five zones for different parts of house, another zone for waterheater (which means I use the boiler all year). The boiler was new five years ago when we bought, gutted, and made initial remodel to house before moving in. Now we have finally saved enough to finish the job (kitchen, floors, and decoration). Having lived here we now have better (well, different) ideas about radiator placement, and I have started in on that.

After chopping up and reassembling zone one I purged and started system (we do need it running to heat the waterheater). It wouldn't hold pressure--dropped in about an hour. I am able to isolate each zone, so isolated the zone I had worked on and charged it with full house water pressure. I do not have a gauge on that, but after several hours I carefully inspected all the solder joints underhouse (I've been there so much I put in rope lights!). No leaks.

During night I began to consider that the pressure relief valve wasn't seating, and sure enough in checking this morning where it discharges outside the house I saw water. Wanting an easier way to check the relief valve discharge (or not) I cut the discharge pipe (downstream of the relief valve) and put in a union (I'd have to do that anyway if I have to replace that valve). It did drip some, and maybe that was part of the problem. Indeed, after fiddling with that the pressure held for three hours.

Several times I've looked at those air relief valves (snifters?) and wondered if they were the culprits. (We've got them on a steam locomotive I operate occasionally, and even there they are a bit mysterious to me.) My system has two of them, one on top of each manifold. Anyway, I've closed them off as you suggest. There is a "drain" **** up at nearly the highest point in the system, and I get water there, not air.

The weird thing is that this problem occurred in conjunction with working on the system. Having had to learn to solder out of a book, I immediately figure I made a bad joint; but I've inspected a couple times and believe I'm okay. Maybe opening, purging, and restarting the system caused the problem elsewhere.

Wendell
 
  #7  
Old 07-04-05, 07:57 PM
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Wendell

For some reason the automatic air vents (auto vents or hi vents as they are called in the trade) often start to leak when the pressure in the system has been relieved for one reason or another. Regarding your leaking relief valve, it seems you got it to seat as it should but keep an eye on it because it will likely leak again. You might want to replace it now during the "off season" or at least get one to have on hand.
 
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Old 07-04-05, 09:23 PM
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Thanks for noticing my addition to this thread and for responding.

I mentioned putting that union in the discharge line after the pressure relief valve. In order to monitor that valve I have left that union un-connected, with a pail on the floor under it. It has remained dry all afternoon, but suddenly this evening the valve opened and let out about half a pint of water.

I have noticed greater changes in pressure since purging and restarting the system. The pressure will get fairly low, and then when the burner kicks on to head the waterheater, the pressure will climb up--and it was in such a spike that the valve lifted. Over the past few years--in normal operation--the pressure really didn't change too much within the cycle.

I don't know what this is all about, but I'd guess there is air in the system, allowing for some water to turn to steam. Any thoughts on this new issue--with wide pressure changes and the pressure relief valve opening? ('Course it is doing its job!).

Wendell
 
  #9  
Old 07-05-05, 06:56 AM
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I think I figured this one out.

My standard response to a potential leak problem is to isolate piping. Well, when I was concerned with a leak on this after reassembly, I had shut off all the zones and had never reopened them. Without those zones open, there was a very limited body of water to absorbe the pressure increase that always comes with temperature increase.

I've opened all the zones. We'll see what happens.
 
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Old 07-05-05, 02:54 PM
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Expansion tank

Do you not have an expansion tank on the system? If not, one should be installed ahead of any flow checks. If you do have one & it is drainabe, try draining it completely. If it is a bladder type tank, drop the boiler pressure to zero & check the air pressure in the tank.
 
  #11  
Old 07-06-05, 07:47 AM
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I do have an expansion tank. It appears not to be drainable. I did not follow your suggestion since the system has behaved properly now for 24 hours.

However, for future reference--how much air pressure should be in it? (I keep my system at 20 psi).

I really think my problem was air in the system--and that that has gone out through the snifter valves. Next time I'll isolate the zones I'm going to cut. That should keep air from being distributed in the whole system. That never occurred to me to do before.

When purging next time, I'll attach the drain hose to the top drain valve--since air rises that may help me purge out all the air better. I did make a special hose out of clear plastic--so I can see the bubbles. That was handy.

This has been a learn by doing process--but thank you very much for your time, tips, and advice. I really appreciate it. I'll be eager to see how that other fellow manages his project on the "removing radiators" thread.

Wendell
 
  #12  
Old 07-06-05, 05:59 PM
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Tank pressure

The tank pressure should be the same or no more than 2# below the system pressure. Twenty pounds is a lot of pressure. It is rare that I see over 15-17. If it works for you without problems, let sleeping dogs lie.
 
  #13  
Old 07-09-05, 05:36 PM
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Well, the fact is it isn't working right. I checked the air pressure in the expansion chamber--it was at 22 psi. I've reduced that to 16 p.s.i. and we'll see what happens. I also flushed the system again--and may have gotten some air out. There still seems to be a lot of pressure change from idle to pump running to boiler coming on--like from 10 to 25--and that isn't the way it was going before I took out those radiators. I still have some radiators to move, and if this thing hasn't settled down by the time that is over with--and system refilled--I'll call the professionals. I've got to get them here anyway to put in a gas line for a gas fireplace and cas cooktop, and have timed this radiator modification just in case I needed them to check my system after I messed with it.

Right now I've pulled the plug on the electrics and am letting the whole thing cool down and will check (again) that it holds pressure when static over several hours.

It will be a while, but I'll report back.

Wendell
 
  #14  
Old 07-09-05, 05:44 PM
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Tank pressure

When you checked the tank pressure, was the boiler pressure at zero? If it was at operating pressure, you may have let air out that you should not have. Tank pressure must be checked & adjusted without pressure against it. If there is a valve between the boiler & tank, you can shut the valve & remove the tank. That way you don't have to drop the boiler pressure.
 
  #15  
Old 07-10-05, 12:21 PM
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Heating system was at zero PSI. I'll check it again though. I've had the heater off for 24 hours--temperature is down to the peg--and the pressure is holding steady. I wanted to check the system for water leaks, and that was really the only way to do it since the pressure changes with temperature. I'm actually taking a break right now from moving more radiators and will flush this zone out and test the whole system again for leaks by watching the pressure before turning the boiler back on. (The zone I'm working on is isolated with valves so the rest of the system is under pressure even though this one is cut open.)

Wendell
 
  #16  
Old 07-10-05, 06:25 PM
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pressure/temperature

With the pressure rising with temperature, it makes me very suspicious of the extrol tank.
 
  #17  
Old 07-11-05, 07:05 AM
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Finally--a good report.

After finishing with the radiator rearrangement and getting that circuit back together I let all the pressure out of the system. Again I checked the expansion tank (is that what you mean by 'extrol tank'?). I even let a bit more air out--taking it down to 18 p.s.i. Then I refilled the system, taking care to really get a good flush and--hopefully--get ALL the air out. I filled it to 15 p.s.i. and then plugged it in.

The boiler had been shut down for nearly 24 hours--checking that it held a steady pressure at room temperature--and it took about three cycles (boiler on and off) to get the water temperature in the domestic hot water tank up to temperature. During those cycles the boiler water would climb up to 170 degrees and the pressure to 20 p.s.i. and back down to 150 and 15 p.s.i. So, I am still getting a pressure increase with temperature increase, but not as much as I was before.

The real test was this morning. Since it is summer, and the heaters aren't coming on, and without demanding hot domestic water all night, I expected that the boiler would have been off all night. This was where I had problems last week in that the temp would have dropped way off and the pressure down to nothing. Anyway, upon checking the pressure this morning I was okay. The pressure was only down to about 12 p.s.i. (I can't remember what the temp was).

The only thing I can imagine different from last week was that I had left too much air in the system upon filling. I'm not sure I understand the physics of what was going on. To me any air in the system would have been the same pressure as the water. But, there is probably a much bigger expansion rate in air as in water with temperature increase, so any air in the system would have expanded greatly upon being heated (causing the relief valve to open) and would inversely have contracted greatly upon cooling, causing the drastic pressure drop.

Letting air out of the expansion tank may have done something. I think letting some air out and attempting to hold the system at 15 p.s.i. is a good thing. Even so, the system had operated okay for six years, so I think the problem had to have been a consequence of something I had done--letting air into the system when I moved those radiators. I think my more careful flushing upon refill was the trick.

I really do appreciate your being here and suggesting things.

Wendell
 
  #18  
Old 07-11-05, 11:03 AM
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A subsequent question:

Is there a checkvalve somewhere in the heating system? One thing I discovered yesterday is that the water moves through the system reverse from what I had imagined. I figured this out by watching the two thermometers installed on either side of the hot water heater heat exchanger. In fact, I had tried to flush the system "backwards" the first time. If there is no check valve this shouldn't have mattered, but maybe there is a check and trying to flush "backwards" may explain how I ended up with air in the system on my first attempt.

Wendell.
 
  #19  
Old 07-11-05, 04:24 PM
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Thumbs up Progress

Glad to hear of your sucess. Yes there are check valves in the system & they should look like this, or similar.
http://taco-hvac.com/products.html?current_category=183
 
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