Tankless Heater with Recirculating System

[gmcmurry]

I have a tankless hot water system in my home with a recirculating pump.
It generally works pretty good.
The system uses two check valves. One to let the cold water in and one in the recirculating loop.
They are 3/4 inch brass flapper type.
I often find the hot water backing up into the cold water supply. Twice over the past many years, I have changed out the check valves and it seem to solve the problem. I guess they just go bad and start leaking after a while.
I have it again now. I am wondering if I should use a different type of valve, maybe a spring type?
At least this time, I am going to reinstall with unions so the job will be easier if it happens again.

Any suggestions would be appreciated.

Greg

PICTURE -- cold water comes in from right on lower pipe. That is the check valve I have replaced a couple of times. Return loop comes out of the pump and through the upper check valve. Then these feed the Tankless. On the output of the tankless I have a small expansion tank.

 

[HWSleuth]

Have you looked into the seating of the flapper in the failed check valves? Any scale or pitting of the flapper Or it’s seat? Does circulating pump run continuously? Water temperature of return water? Has expansion tank been pressurized to match incoming cold water pressure? Expansion tanks don’t come pressurized to match commercial DL water supply pressures. Flapper type check valves will seal better when vertically installed in lines where you are restricting back flow.

 

[gmcmurry]

Great questions...

• The last time I replaced the check valve I could see it was worn a bit but not pitted.
• The temp of the return water is generally hot enough that the heater says off for long periods of time.
• I have a system that turns off the pump when we are not home. These days, that is not often but normally its off about 8 hours a day. Think I should try leaving it on?
• As for the tank, I don't think I have checked it lately nor do I really know how to set it to begin with. If I have 65 psi water pressure, should I measure 65 psi on the bladder when the tank is empty? I could use some advice here.
• Not sure how difficult it would be to install the check valves vertically. That would mean re-plumbing that whole area. That's why I asked if I should consider a spring type check valve.

Thanks for the reply.

 

[Mitchell-DIY-Guy]

I have a lot of experience with check valves from my days owning a car wash...everything from small ones on small tubing to larger ones operating in 1200PSI conditions.

All check valves are wear items. Most spring valves will have some kind of rubber seal or seat and those will wear out over time. They also have a "cracking pressure" which is the minimum force requires to open or "pop" the valve open. Even with a spring type with low cracking pressure you will experience a pressure drop...You may also need to upsize the check valve relative to the pipe size in order not to otherwise restrict the flow.

You'll probably get less wear with a stainless steel check valve, and you can find those that are easy to rebuild. I used to keep spares around, as well as spare parts to rebuild them as the valves always needed attention [in a car wash]...

 

[breplum]

Caleffi makes a brilliant union flow/spring check valve

 

[gmcmurry]

That looks like a beautiful piece. I am going to rebuild using these. Thanks for the advice.

Most of my house is 1" copper. The installer opted to put a 1" check valve on the incoming cold water then reduce to the recirculating loop which is 3/4. The check valve in the loop is 3/4".

Wouldn't it be more logical to reduce to 3/4" in the incoming water then use two 3/4" check valves instead?

Greg

 

[Mitchell-DIY-Guy]

1" copper is not all that common throughout a home; generally you may have 1" copper coming in, and then branching off to ¾" supply lines then to ½" branch lines.

If you would have the need for the check valve on a ¾" line, my suggestion would be to use a 1" check valve (upsize) to minimized your pressure and flow loss.

If you have 1" lines, don't know if that's much necessary. Like all other check valves it will need periodic rebuilding.

 

[HWSleuth]

Use a 1” IPS check valve with Sharkbite fittings (2). Would still like to know condition of existing internal seat and disc.

 

[gmcmurry]

Caleffi makes a brilliant union flow/spring check valve
View attachment 27085

I know this is an old thread but I wanted to follow up.
I installed a 3/4" and 1" Caleffi in my system and they have been fantastic.
Lately, I thought I might purchase replacement valve insert but can't find them anywhere. SupplyHouse.com says they cannot source them and Caleffi doesn't want to sell directly without a $100 minimum.
It's easier to buy the whole thing. Then I can get new washers and everything.

Greg