No check valve on HW return line - is this OK?

[DIYQuestionGuy]

Trying to troubleshoot why my kitchen sink on 1st floor now takes forever to get hot water after water heater was replaced. I have 2 story house, water heater in basement. A return line is plumbed into drain valve of water heater. I'm the original home owner (19 years). After having water heater replaced it seems that something has changed. Previously, we seemed to receive hot water pretty quick at kitchen faucet. Now it takes several minutes. Huge waste of water, especially first thing in morning. Bathrooms on 2nd floor get hot water pretty quick, and they're farthest away from water heater.

The return loop appears to be passive, no pump in system (I've looked under all vanities). There does not appear to be a check valve in the loop on return line coming into water heater. Should there be? Would this cause the return loop to not work effectively, i.e. improper circulation? That's my theory, but I'm not a plumber. I'm hopeful, wondering if installing a check valve would fix my kitchen sink issue. It used to be work fine. Picture included.

 

[Twowaxhack]

With the pump running 24/7 you don’t need a check valve in the return.

If the pump cycles on/off you would need a check in the return.

With the pump running your Ksink should get hot pretty quick. With the pump off is when you’d have trouble.

 

[Twowaxhack]

That guy used $50 worth of press fittings on that return

The relief line isn’t terminated properly.

 

[MicEd69]

It appears you have a "Gravity Hot Water Recirculating System" that does not have a circulating pump, correct?

Those are not really efficient in getting hot water quickly to all fixtures. I'm assuming the original return line had a check valve. Without a check valve, when you pull water from the water heater, it will be coming from both the top and the bottom of the water heater. So, you will be receiving colder water from the newly supplied water going into the water heater through the cold-water inlet dip tube and hot water from the top of the water heater outlet. That would mean that your hot water at all your fixtures will vary as the flow from the water heater will be a mixture of hot water and colder makeup water to the water heater.

 

[DIYQuestionGuy]

It appears you have a "Gravity Hot Water Recirculating System" that does not have a circulating pump, correct?

Those are not really efficient in getting hot water quickly to all fixtures. I'm assuming the original return line had a check valve. Without a check valve, when you pull water from the water heater, it will be coming from both the top and the bottom of the water heater. So, you will be receiving colder water from the newly supplied water going into the water heater through the cold-water inlet dip tube and hot water from the top of the water heater outlet. That would mean that your hot water at all your fixtures will vary as the flow from the water heater will be a mixture of hot water and colder makeup water to the water heater.

Correct, this is gravity hot water recirculating system, hence no pump. It seemed to work just fine from what we could tell until the water heater was replaced. I suspect there was a check valve originally but installer did not put one back in. I'm wondering if this is why I'm now experiencing the longer wait time for hot water at the kitchen sink. Your explanation is what I'm suspecting. Would this also cause the hot water heater to cycle more often than it should? I'm on my 3rd hot water heater in 19 years. The 2nd and 3rd, no check valve. I can't say for sure about 1st one but I'm guessing it had one because it would have been installed by plumber who installed the return line (assuming he knew what he was doing). Can't say for sure about the other guys who contract with the utility company.

 

[DIYQuestionGuy]

That guy used $50 worth of press fittings on that return

The relief line isn’t terminated properly.

No pump, this is gravity loop. May I ask what's wrong with termination? I don't doubt it's wrong but would like to know why. Thank you.

 

[Twowaxhack]

No pump, this is gravity loop. May I ask what's wrong with termination? I don't doubt it's wrong but would like to know why. Thank you.

It needs to be piped like your old heater at the return and most likely have the heat trap nipple removed on the hot side outlet.

I’d remove the heat nipple first and see what happens.

It’s terminated too far from the floor.

 

[Twowaxhack]

Or just add a pump.


The pump is not always located at the water heater. It’s typically installed anywhere in the return line, usually at the water heater but that’s not a rule.

 

[DIYQuestionGuy]

Or just add a pump.


The pump is not always located at the water heater. It’s typically installed anywhere in the return line, usually at the water heater but that’s not a rule.

Thanks. Appreciate the ideas. I've been going back and forth on whether adding a pump would be beneficial. At the least it appears a one way valve is needed on return line. I'm assuming the pump would move more volume of water and result in quicker hot water?? The gravity system (without pump) seems to work OK (or did previously)..... Upon further inspection I'm not confident the return line is even tied into kitchen sink. I can see it coming down from 2nd floor bathrooms but I don't see anything like this near kitchen sink supply. I guess they could tie in the wall somewhere on 1st floor but not sure.....

 

[MicEd69]

Bathrooms on 2nd floor get hot water pretty quick, and they're farthest away from water heater.

You could be right in your last post that the kitchen isn't in the recirculation loop. The original idea may have been to loop just the farthest fixture. Then the water would be at least warm to the tee to the line going to the kitchen. Passive systems are nice as they don't use electricity, but they are limited as their motive force is just the convection of the "hot" water. And without a check valve at the drain valve connection, the water will be drawn from both pipes to the fixture resulting in cooler water everywhere and more cycling of the water heater.

And as Twowaxhack indicated, this new water heater may have integral heat traps that are meant to limit hot water from migrating up and out of the water heater.

 

[Twowaxhack]

Gravity systems work if everything is proper. That can be tricky sometimes.

The real energy hog is circulation hot water 24/7.

To have an efficient system you’d need a pump that only operated when you needed hot water. Timers, smart plugs, manual push buttons, motion sensors etc are used. Some learn your schedule, etc.

The pump is easy to install and uses very little power,

 

[DIYQuestionGuy]

You could be right in your last post that the kitchen isn't in the recirculation loop. The original idea may have been to loop just the farthest fixture. Then the water would be at least warm to the tee to the line going to the kitchen. Passive systems are nice as they don't use electricity, but they are limited as their motive force is just the convection of the "hot" water. And without a check valve at the drain valve connection, the water will be drawn from both pipes to the fixture resulting in cooler water everywhere and more cycling of the water heater.

And as Twowaxhack indicated, this new water heater may have integral heat traps that are meant to limit hot water from migrating up and out of the water heater.

Thank you.

 

[Twowaxhack]

One of the troubles of a gravity system is the cracking pressure required to open the check. Holes can be drilled in swing checks but it’s a dance.

 

[DIYQuestionGuy]

Gravity systems work if everything is proper. That can be tricky sometimes.

The real energy hog is circulation hot water 24/7.

To have an efficient system you’d need a pump that only operated when you needed hot water. Timers, smart plugs, manual push buttons, motion sensors etc are used. Some learn your schedule, etc.

The pump is easy to install and uses very little power,

Thank you and MicEd69. Good info. Seems like installing check valve is good first place to start although it likely won't fix my kitchen sink issue

One of the troubles of a gravity system is the cracking pressure required to open the check. Holes can be drilled in swing checks but it’s a dance.

You literally were reading my mind. Based on my limited research and knowledge I have read about possible issues with check valves. Do you have certain type you'd recommend? I'm not very familiar with different types so appreciate the recommendation.

I'm leaning towards starting with installing a check valve on return line just before termination. Mainly because I can't imagine the return loop is really working as designed without it (can't hurt, right?).

I'm not familiar with heat trap nipples. That's new to me. I'll have to look into that but given how new my water heater is I'm assuming it would have one unless installer removed it??

I've watched several videos on the recirc pumps. If I were to go that route would I install that on the return loop or on the hot water outlet on top of water heater?

At the end of the day I'll probably hire a plumber but I like to know what my options are ahead of time and pros/cons. Also, honestly, it seems hard to find good tradespeople these days......

 

[Mitchell-DIY-Guy]

@DIYQuestionGuy i had a perfectly functioning passive “thermosiphon” circulating hot water system in my home in Michigan for the 27 years I lived there. It lived through three different water heaters but I was the guy that changed them. The water heater was in the basement and the return line came from the primary bathroom on the second floor. As the water flow in this system is “low and slow” it wasn’t instant hot water but pretty darn quick. Unfortunately the guest/kid’s bathroom on the second floor wasn’t in the loop. I wasn’t concerned with “efficiency” as the piping was on interior walls within the building envelope; since we used heat from September 1 through May 31 (Michigan!) the latent heat wasn’t really wasted.

The key to the system were several things: first you need “head”; and a heater in the basement and loop return on the 2nd floor is exactly that. Hot water rises, you need a place for it to rise to. Then you need a horizontally mounted swing check valve installed on the return line near the water heater. Swing check since they have no cracking pressure and horizontal mounting so it functions properly. The swing check keeps flow in the proper direction; flow is OUT from the top of the tank, rising to the loop return on a higher floor, and returning to and flowing into the bottom of the tank. I also had a shut off to both disable the system and for servicing.

Once in those 27 years, I replaced the swing check. I could tell it wasn’t functioning properly since the wait for the hot water had increased. It was a $10 brass part.

 

[Twowaxhack]

Every check valve has a cracking pressure.

 

[Mitchell-DIY-Guy]

Every check valve has a cracking pressure.

Nobody likes a smart**, and don't confuse the original poster!

A spring check valve has a cracking pressure, and they are often rated as such by the manufacturer. All it means is when the spring loaded check "cracks"; it doesn't mean full flow or the rated Cv of the valve. Some plain spring check valves have low (< 2 psi) cracking pressures but that doesn't mean they'll flow anything appreciabley at that pressure.

While technically a swing check may indeed have some measurable cracking pressure, I don't think you'll find a cracking pressure rating on a swing check. That means it's close to zero; irrelevant. Also, most of the swing checks for these relatively benign domestic water applications (as opposed to some chemical or industrial processes, or high pressure) don't even have O-rings or other kinds of seals like a spring check; just a brass (if that's the valve material) swing gate. That's the $10-$15 ones you'll find at the big box stores which will be perfectly suitable in this application.

In a thermosiphon recirculating hot water system, you will generally see very simple piping as shown in the diagram I posted earlier. The swing check must be mounted horizontally. That diagram doesn't show a shutoff which is always a good idea.

 

[DIYQuestionGuy]

@DIYQuestionGuy i had a perfectly functioning passive “thermosiphon” circulating hot water system in my home in Michigan for the 27 years I lived there. It lived through three different water heaters but I was the guy that changed them. The water heater was in the basement and the return line came from the primary bathroom on the second floor. As the water flow in this system is “low and slow” it wasn’t instant hot water but pretty darn quick. Unfortunately the guest/kid’s bathroom on the second floor wasn’t in the loop. I wasn’t concerned with “efficiency” as the piping was on interior walls within the building envelope; since we used heat from September 1 through May 31 (Michigan!) the latent heat wasn’t really wasted.

The key to the system were several things: first you need “head”; and a heater in the basement and loop return on the 2nd floor is exactly that. Hot water rises, you need a place for it to rise to. Then you need a horizontally mounted swing check valve installed on the return line near the water heater. Swing check since they have no cracking pressure and horizontal mounting so it functions properly. The swing check keeps flow in the proper direction; flow is OUT from the top of the tank, rising to the loop return on a higher floor, and returning to and flowing into the bottom of the tank. I also had a shut off to both disable the system and for servicing.

Once in those 27 years, I replaced the swing check. I could tell it wasn’t functioning properly since the wait for the hot water had increased. It was a $10 brass part.

Thank you for your post. Your set up sounds pretty much exactly like mine (minus the check valve). I was starting to doubt myself after having several plumbers tell me there must be a pump in the loop for it to work, and that gravity systems don't work. Mine DID work for several years, until water heater was replaced. Other than the water heater being replaced the only thing I see that's presumably different is no check valve in the return line. I'm planning to install a swing check valve horizontally on the return line to see if that improves my situation. I've not soldered (sp?) before so I'm considering shark bite connection. Since it's not behind a wall, and I call visually inspect it often I'm thinking that should be OK. I know shark bites can be controversial.

Question for you - Twowaxhack mentioned something about removing the heat trap nipple. This was new to me. Did you have to remove this in your system when you installed your water heaters? I can't tell if mine has been removed or not as I'm not exactly sure what I'm looking for or if it really matters (pic attached).......

 

[Twowaxhack]

Nobody likes a smart**, and don't confuse the original poster!

A spring check valve has a cracking pressure, and they are often rated as such by the manufacturer. All it means is when the spring loaded check "cracks"; it doesn't mean full flow or the rated Cv of the valve. Some plain spring check valves have low (< 2 psi) cracking pressures but that doesn't mean they'll flow anything appreciabley at that pressure.

While technically a swing check may indeed have some measurable cracking pressure, I don't think you'll find a cracking pressure rating on a swing check. That means it's close to zero; irrelevant. Also, most of the swing checks for these relatively benign domestic water applications (as opposed to some chemical or industrial processes, or high pressure) don't even have O-rings or other kinds of seals like a spring check; just a brass (if that's the valve material) swing gate. That's the $10-$15 ones you'll find at the big box stores which will be perfectly suitable in this application.

In a thermosiphon recirculating hot water system, you will generally see very simple piping as shown in the diagram I posted earlier. The swing check must be mounted horizontally. That diagram doesn't show a shutoff which is always a good idea.

All check valves have a cracking pressure.

In a gravity hot water recirculating system it matters.

You don’t have to like it or agree but it is a fact.

 

[Twowaxhack]

Thank you for your post. Your set up sounds pretty much exactly like mine (minus the check valve). I was starting to doubt myself after having several plumbers tell me there must be a pump in the loop for it to work, and that gravity systems don't work. Mine DID work for several years, until water heater was replaced. Other than the water heater being replaced the only thing I see that's presumably different is no check valve in the return line. I'm planning to install a swing check valve horizontally on the return line to see if that improves my situation. I've not soldered (sp?) before so I'm considering shark bite connection. Since it's not behind a wall, and I call visually inspect it often I'm thinking that should be OK. I know shark bites can be controversial.

Question for you - Twowaxhack mentioned something about removing the heat trap nipple. This was new to me. Did you have to remove this in your system when you installed your water heaters? I can't tell if mine has been removed or not as I'm not exactly sure what I'm looking for or if it really matters (pic attached).......

View attachment 42245

You’ll have to remove the heat trap nipple.

You’ll have to have enough head pressure to open the swing check.

If you don’t, you’ll need to drill a hole in the check to allow circulation and allow enough circulation to have a functional system that serves its intended purpose.

Drill the hole too small and it won’t work, drill the hole too large and you’ll get reversed flow.

It’s a dance, just like I said in an earlier post. It has to be customized in SOME cases. They all can be different.