Hot Water recirculation mystery

[kcbaltz]

I've lived in my current house for several years and the hot water has always arrived within seconds, no matter how far from the hot water tank, so I always figured the house must have a recirculation system. And even though I found the pipe into the bottom of the water heater that I'm assuming is part of that recirculation, I have never found a pump. Earlier this year, we had a new shower installed which involved turning water off, some draining, etc. and afterwards, the hot water was slow to appear at faucets for a week or so but eventually returned back to appearing quickly. The only step I tried to fix this was to run all the hot water from everywhere in the house at once.

Now, back in October, I had to have my hot water heater replaced and the hot water circulation has not restarted more than a month later, no matter what I've tried. I asked the installer and he agreed there's a recirculating line and that he had reconnected it, but couldn't explain why it had ever worked without a pump. It's a single-story house and my understanding is that siphon systems generally are installed with basement water heaters whereas ours is in the garage, same level as the rest of the house. The only change in the plumbing I can see is that there used to be a ball valve on the return to the water heater which was not put back. But that valve was always open as far as I know.

One observation of the plumber was that when I turned on the kitchen sink, he noticed the return pipe heated up immediately, suggesting it was pulling in the wrong direction. I'm wondering if maybe there was some kind of check valve before that wasn't replaced?

Any thoughts on how to get the water recirculating again?

 

[Mswlogo]

I don’t know much about it but there is another recent thread talking about gravity driven recirculation systems.

Also I recently fixed an issue with new touchless faucets that basically was a direct connection between hot and cold when they were off but left in a mixed position. Water was frequently hot instantly all over but was inconsistent. I added check valves at each touchless faucet to fix it.

 

[Sponsor]

 

[Sylvan]

I have a return recirculation on my hot water heater and it feeds the 2nd floor with almost instant HW without any circulator.

It is basic science HW rises, and cold water is denser and thus flows down the line and fallows the lighter HW to circulate just like the old days hydronic systems.

 

[kcbaltz]

I have a return recirculation on my hot water heater and it feeds the 2nd floor with almost instant HW without any circulator.

It is basic science HW rises, and cold water is denser and thus flows down the line and fallows the lighter HW to circulate just like the old days hydronic systems.

I agree the science makes sense. My mystery is really "what changed?" Why did installing a new Water Heater stop the recirculation. Is it possible the old recirc return line had some kind of check valve on it that was needed to make things work? I know it had a ball valve that was usually open, not sure what that was for.

 

[Mswlogo]

I agree the science makes sense. My mystery is really "what changed?" Why did installing a new Water Heater stop the recirculation. Is it possible the old recirc return line had some kind of check valve on it that was needed to make things work? I know it had a ball valve that was usually open, not sure what that was for.

More likely the new tank has a check valve stopping it.

 

[John Gayewski]

With a gravity system you do need a check valve on the return line. Without a check valve you should be getting cold water injected into your hot water as the cold water enters the bottom of the tank.

Also with gravity recirculation there should be a means to bleed the recirc line. You need a valve between the recirc and the heater with a drain in it. If the line has been completely drained there's almost no amount of bleeding that will fill it back up with water. (theoricially the line will eventually fill back up with water as the air dissolves back into the water, but there is no good way to know how long this could take). Since there is no pump to help drive water back through the recirculation line you need to manually bleed the air. Even with a pump there are situations where no water can flow as there's too much air.

 

[kcbaltz]

With a gravity system you do need a check valve on the return line. Without a check valve you should be getting cold water injected into your hot water as the cold water enters the bottom of the tank.

Also with gravity recirculation there should be a means to bleed the recirc line. You need a valve between the recirc and the heater with a drain in it. If the line has been completely drained there's almost no amount of bleeding that will fill it back up with water. (theoricially the line will eventually fill back up with water as the air dissolves back into the water, but there is no good way to know how long this could take). Since there is no pump to help drive water back through the recirculation line you need to manually bleed the air. Even with a pump there are situations where no water can flow as there's too much air.

In this case, the return goes to the bottom of the tank where the hose bib for draining is attached. Turning on the water in the kitchen causes this return pipe to heat up immediately, so I don't think there's a danger of cold water flowing into the siphon loop.

Could I use the hosebib as a bleed? I'm thinking it'll mainly just drain the tank without forcing the loop to flush any air out. I've tried running all the hot water outlets in the house simultaneously to bleed it but that didn't seem to work.

 

[John Gayewski]

In this case, the return goes to the bottom of the tank where the hose bib for draining is attached. Turning on the water in the kitchen causes this return pipe to heat up immediately, so I don't think there's a danger of cold water flowing into the siphon loop.

Could I use the hosebib as a bleed? I'm thinking it'll mainly just drain the tank without forcing the loop to flush any air out. I've tried running all the hot water outlets in the house simultaneously to bleed it but that didn't seem to work.

You need a valve between the tank and the recirc with a drain

 

[kcbaltz]

You need a valve between the tank and the recirc with a drain

The recirc return attaches to a tee with one end going to a hose bib and the other into the bottom of the tank. Are you suggesting I drain that without turning off the cold supply? And do it until I get some kind of air release/sputtering? I know ideally I'd want to block the connection to the hot water tank and just drain the recirc so it pulls from the hot supply line but it's not currently plumbed that way.

 

[Tuttles Revenge]

if the pump is still kicking you should be able to hear it.

 

[John Gayewski]

if the pump is still kicking you should be able to hear it.

Gravity

 

[John Gayewski]

The recirc return attaches to a tee with one end going to a hose bib and the other into the bottom of the tank. Are you suggesting I drain that without turning off the cold supply? And do it until I get some kind of air release/sputtering? I know ideally I'd want to block the connection to the hot water tank and just drain the recirc so it pulls from the hot supply line but it's not currently plumbed that way.

Your recirc has been setup incorrectly. From the tank you need a nipple, then a valve, then a nipple, then a tee. The straight portion of the tee gets your drain which is for the water heater and the recirc line. The side inlet of the tee then gets a nipple and a check valve, the recirc line goes after the check valve.

 

[John Gayewski]

 

[kcbaltz]

Thanks, that makes a lot of sense. I'll see about getting that implemented.

 

[kcbaltz]

One more thing I can't figure out: even if the previous setup had the ability to flush the recirc line, I never used it and yet the system recovered on its own after a few weeks each time it was disrupted but this time it's been 2 months. Would a missing check valve on the recirc be enough to explain the difference? The plumber who installed the heater says there was no check valve before.

 

[John Gayewski]

One more thing I can't figure out: even if the previous setup had the ability to flush the recirc line, I never used it and yet the system recovered on its own after a few weeks each time it was disrupted but this time it's been 2 months. Would a missing check valve on the recirc be enough to explain the difference? The plumber who installed the heater says there was no check valve before.

I don't know what to tell you. A recirculation line needs to have a check valve or there's no way for the water to know which way it should travel.

If you have a plumber he should be able to figure this out fairly easily.

 

[Hogan]

I don't know what to tell you. A recirculation line needs to have a check valve or there's no way for the water to know which way it should travel.

If you have a plumber he should be able to figure this out fairly easily.

I just experienced this when our new 75 was installed and the guy plumbed the recirc lines into the cold water inlet of the tempering valve and he didn't realize that the valve inlet itself didn't already have a check valve. Cold water drew straight up the recirc lines when we opened the hot tap up on second floor. Luckily the addition of a simple swing check valve solved the issue

 

[Jeff H Young]

Id hook up your heater the way it was but personaly never built gravity feed and wouldnt take ownership / responceability for its performance. I install a pump a check valve and a method of bleeding off air on every single one I built since having a problem bleeding off air 20 years ago. unless I was installing to anothers specification a drawing like on a school or something Ill just follow orders