Troubleshooting hot water heating sysytem


Old 03-13-19, 09:48 AM
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Troubleshooting hot water heating sysytem

I have entrained air in the water of my heating system. I have bled the system several times, but cannot eliminate the air. Initially the air is gone following a bleed ,but within minutes it returns and I can hear a light "gurgling" or "swishing". It does not appeat to effect the system or effect the systems ability to heat. However, it is mildly noisy, irritating and may eventuallu lead to other problems.

I have visually inspectred the system for tell tale leak, expecting to te see discolouration or calcium deposits on any joint or solder joint. All leak point appear to be sound.

I also found that I could effect a temporarary solution by venting the air from a 3/4 inch water supplied bath tap located immediately on the floor above the boiler in our main bathroom. A short spurt of air mixed water would quickly turn to a solid water flow and the "swishing" would stop temporarily, but return some minutes later or when the heating next cycle ON.

I have come to suspect a my 7 year old Xtroll Model 30 expansion tank.

The sytem in summary:

Hard, but filtered and softened well water is heated in a 10 year old boiler by oil. The hot water is kept very hot to reduce heating cycles and oil use. The expansion tank is located in a horizontal configureation about 12 inches above the hot water feed from the tank. Above this feed line it is cross feed to the cold water in flow side and controlled by a valve that is left open between the hot and cold water lines. The hot water then travels through a heating thermostat temperature controlled zone valve that then is passed through a pump leading to a water heat exchanger located in an adjacent air handler where pass through air is distrubeted throughout the 2400 sq ft house very effectively.

Untill 3 years ago the water heating system supplied more that adequate hot water and heating water without incident or concern.

At that time a contractor replaced my zone valve and it was at this time the air entrainment started to occur. I had routinely bled the air from the system at the beginning of each heating season only to have the phenonema re occur as described. During the summer season when heating is not required there is no evidence of air entrainement in the system.

Some months ago I began to think it was the zone valve for obvious reseons, but being only 3 years old I started athread here on this topic. I learned to replace this myself and subsequently resoursed the correct zone vale which I bought and keep as a spare. However, as I learned about zone valves and auxilary flow pumps I realize that the neither the zone valve not the pump were the likely problem.

I have now begun to suspect my expansion tank.

1.Could the expansion tank be the problem?
2. If so how can I test it?
3. Given it's culpability, how do I replace it? I know I can buy a repalcement new tank for around $125.

I can attach photos and a diagram if helpful

Sorry for the lenght of the desciption. Any help and advise will be greatly appreciated

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Old 03-13-19, 11:56 AM
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First off your extrol tank would cause a high pressure problem causing the relief valve to go off at 30PSI.

Next, your potable or faucet water are completely different than the water in your boiler and heating system. You do not want boiler water coming out of your faucets for obvious reasons. You may get your domestic hot water from a coil inside your boiler but the two and completely separate sources of water. Your coil is heated by the surrounding boiler water as fresh water runs through it and out to the faucets.

There are specific ways to bleed your system and if not done right air will continue to return. Once a system is bled the only way for air to enter your system because it is a closed system is through the introduction of fresh water through your feed valve or a less likely way is from a defective air vent sucking air in when the pump comes on or a bad gasket at the pump where it's possible that air could be sucked in but not be enough to leak water.

My guess is it is not being bled properly since this started after a ZV was replaced. On another note there is no need and should not be done, to bleed your system every year as a form of maintenance. Every time you open the system you run the risk of air entering which is the boilers worst enemy.

Pics of your boiler and near boiler piping would be helpful. A sight posted below are some options of extrol tanks.

You also mentioned an air handler. Do you have baseboard also.

Hope this helps a little.
Old 03-14-19, 08:12 AM
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Thanks Spott,

Your reply was very helpful! You scared me a little with your comment on the seperate sources for potable and heating water. as the hot water to my faucets appear to come from the same single outlet on the top of the boiler. A "T" is in the hot water outlet about 18 inches above the boiler. The horizontal line goes to the ZV and the vertical line feeds the numerous hot water taps throughout the house.

I was probably confusing in my original post implying that the cold water is some how conneted to the boiler system. Of course, as you said correctly, it is not and is on a completely seprate system. strangely though this feed also exibits air entrainment, but when released from the cold water tap on the next floor immediatelty above the boiler, it has no impact on reducing the "swishing" noise when heat is demanded.

Your comment about the pump is interesting as I have heard short bursts of bubbling from the pump although no evidence of water leaks. I dismissed the pump as a problem source initially as I thought it maybe temporarily cavitating as air from another source passed through it. From your comment I now realize that the pump maybe suspicious. The pump is a Taco Circulator. The pump is a cartridge type easily replaced without draing the lines by removing 4 small bolts on the housing and replacing the cartridge and "O" ring. It is also the original pump which is about 10 years old. Perhaps I should first repalce the cartridge pump before further troubleshooting?

I have attached photos
Thanks again

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Last edited by PJmax; 03-14-19 at 11:05 PM. Reason: resized pictures/added closeup
Old 03-14-19, 04:04 PM
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Does Air Rise In Hydronic Systems?

Rather than start at highest point in hydronic system where air is most likely to collect, comments in many DIY threads focus on things at the boiler level, lowest point in system.

It is wishful thinking to expect bleeding air at boiler level will remove air in heating elements at higher levels. Air scoops near the boiler have their limits.

Well designed hydronic systems often use Baseboard-Tees on heating elements to attach manual or automatic air vents on elements on each loop.

Old 03-14-19, 07:18 PM
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I am a bit confused myself after seeing your pics. It looks like you have a hot water heater and not a regular boiler. That pump you're showing looks like a Bronze circulator made for potable water and not heating water, yet your extrol tank is for heating systems and not potable water.

Is that system for heat or hot water. With the ZV's I'm guessing heat but what are you using for hot faucet water.

One important point about the pump. It must be isolated even when just removing that cartridge. That is a WET ROTOR pump and there is water in that cannister. The same water that goes through your system. It's not like the older style pumps where the motor was separate from the volute that connected to the piping.

It looks like a Bronze pump which is not needed on a heating system but they may have had a reason. Below is a sight that will show you your options and give you some info that may be helpful.
Old 03-16-19, 01:47 PM
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Hi Spott.

I am sorry for the confusion!

The tank is a "hot water tank" and not a boiler. I did not realize that there was a difference in application.

The tank is a John Woods JWF 507 and the pump is a TACO Model 008 BC6.

On original instalation I was told that he tank was over sized to 50 usg to provide sufficient hot water to both the heating system and various hot water faucets throughout the house.

Both the seperate cold water system and the hot water tank supply system are potable water from my well, The well is filtered for particlate and humus using seperate 0.5 micron and activated charcoal filters. the combined water is then passed through a softener that successfully and adequately softens the water, although I have not measured the post softener hardness. Simple observation tests, i.e. no tank bottom deposition and no softner venturii contamination on back wask confim high quality of water. This water then is fed seperately to the cold water faucet outlets system throughout the house and the hot water heater.

There is no cross over from the hot water supply line to the cold water faucet supply system. However there is a cross over, controled by a ball valve between the cold water supply to the hot water tank and the hot water outlet pipe on the same tank. This valve is left open.

The used hot water exiting from the air handler heat exchanger is returned to the hot water tank "cold" water supply line.

Would you kindly confirm your comments about the pump cartridge removal relative to the identifed TACO pump.

Two of the photos exibit considerable scaling on the copper lines above the tank. Could these be the source of air entry? Would it be prudent to replace these lines before I proceed with further trouble shooting?

Do you have any advise on whether or not I need to resolve any problen that might arise from the pump and Xrtol tank usages relative to potable water.? Is there a problem in using potable water for heating?

Many Thanks,

Old 03-16-19, 03:38 PM
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I see some troubling items in your photos. The copper pipe joints that show white or greenish scale on the exterior - that is caused by the joint leaking. That needs to be fixed.

Using a hot-water heater in place of a hot-water boiler for space heating is sometimes encountered, but not a good idea, at least in my opinion. I know you are located in Canada, but in many U.S. locales that would be prohibited. A heating boiler is usually approved for such use by the American Society of Mechanical Engineers (ASME) - not so for a water heater.

There is a hole in the exhaust flue. Not good.
Old 03-16-19, 06:24 PM
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As gil pointed out and I agree using a hot water heater for both heat and domestic water, although done at times I don't think is a good idea. That being said, if done it must be piped properly to keep the heating water from getting into the potable water generally with the use of check valves.

" Would you kindly confirm your comments about the pump cartridge removal relative to the identifed TACO pump."

If you mean proof by confirming, click on the sifgt in post #5 and see if you can find a cutaway version somewhere. The only other confirmation I can give you is 42 yrs. in the business. My sincere advice is to not open it up without isolating it and letting the water cool down. Hopefully you have shutoffs on both sides so you don't have to drain the system.

That scale and green crud is surely a sign of leaking which should be fixed and could be the cause of air.

If pics are possible of the whole tank and piping it might be helpful. If not piped right then when you use the faucet and fresh water feeds into the tank it could be getting into the heat side bringing air. Thing with using a hot water tank for heat and hot water is a tank does not have a long life compared to a boiler due to the constant feeding of fresh water and the high heat from the burner on the tank.

BTW because the tank is used for both that is why you have the BRONZE pump and not the regular cast iron. In that tank you have an anode rod that should be checked and changed periodically to prolong the life of the tank. You can google it to see the purpose of it.
Old 03-16-19, 08:17 PM
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A domestic water heater that doubles as a hydronic boiler will always commingle the domestic water with the radiator water.

You might get away with a system like that when the space to be heated is small and more specifically the water heater can deliver enough BTUs to heat the space (rooms)

Water heater burners are of much lighter duty (often stamped sheet metal) than space heating boiler burners (cast iron).

Last edited by AllanJ; 03-16-19 at 08:32 PM.
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