Hydronic Radiant Flooring + Navien Tankless - cold water - need help

[CuttyOX]

Hi,

I have a Navien NPE-240A tankless water heater that is connected to an external hot water recirculation system that goes to my hydronic radiant floor system.

Last week my hot water was not staying hot, if I hadn't used the water it would get hot for about 30 seconds and then get luke warm/cold. I thought it could be an issue with my Navien so I cleaned the filters and flushed the system out with vinegar and then with flow-aid the 2nd time since vinegar didnt work. The issue wasn't fixed and after doing some digging I had a feeling it may be a crossover issue because water was still coming out of my bathroom sink and shower when I had the faucets turned to hot before I drained the system and the hot water line off.

I turned the valve off to my external recirculation pump and now I get hot water at every fixture.... Hot water is working fine now but I won't be able to heat my basement floors with the system off.

Had two plumbers come out earlier today to give an estimate. 1st one wasn't sure and thought I need to get a hydronic expert out, 2nd one confirmed my findings and that cold water seems to be mixing with the hot water pipes which is why my hot water won't stay hot.

He thinks it could be that I need an additional check valve but waiting for him to talk with some colleagues and get back to me. I asked why this would have worked in the past (since the house was built in 2014) and not have ran into this issue previously and he couldn't tell me but thinks adding this additional check valve will help.

Any thoughts on what could have failed? Would like to figure out the issue without installing an additional check valve if possible

 

[CuttyOX]

 

[Sponsor]

 

[Fitter30]

Using dhw for heating also is a bad idea. Is the gpm flow not making the minimum flow rate? Probably a bad check in the return line. Possibly 9-1

 

[CuttyOX]

Using dhw for heating also is a bad idea. Is the gpm flow not making the minimum flow rate? Probably a bad check in the return line. Possibly 9-1

Thank you! In regards to the minimum flow rate - it is typically in the 2.X gallon range when I have my fixtures on

 

[WorthFlorida]

Hi,

.............. I had a feeling it may be a crossover issue because water was still coming out of my bathroom sink and shower when I had the faucets turned to hot before I drained the system and the hot water line off.

I turned the valve off to my external recirculation pump and now I get hot water at every fixture.... Hot water is working fine now but I won't be able to heat my basement floors with the system off........

Did you turn off the cold water where the crossover (check) valve is? It seems that it is stuck open.

 

[Fitter30]

Brand and model of heat exchanger? Is the pump between heat ex and heater bronze or stainless? Floor heat how many feet of pex and size? Is there a control for priority dhw?

 

[Breplum]

It is the internal check valve. Well known issue. Even now with the latest 240 A2.

 

[CuttyOX]

It is the internal check valve. Well known issue. Even now with the latest 240 A2.

Hi - would that make sense if I am getting hot water consistently when I turn the valve off to my external recirculation pump?

 

[CuttyOX]

Brand and model of heat exchanger? Is the pump between heat ex and heater bronze or stainless? Floor heat how many feet of pex and size? Is there a control for priority dhw?

Hex - Brazed plate heat exchanger blk14-20D. Not sure about any of your other questions in regards to the control for priority, feet of pex and size.. Pump between heat exchanger (Looks like I have two pumps one is Grundfos UP 15-42 BUC7 which says its a bronze sweat mount pump and has an internal check valve. The other is a Liquidus water circulating pump lpc15-5 sncf - this one says its a cast iron.. After looking both of these up I think they both have internal check valves.

 

[CuttyOX]

Did you turn off the cold water where the crossover (check) valve is? It seems that it is stuck open.

I have previously turned off the cold water - right now I just have the valves turned off at the system that feeds my hydronic radiant floors at the first recirculating pump (the liquidus one I mention above)

 

[Fitter30]

Pump next to the boiler top valve is almost closed. That valve should be used for flow control it's a shut off valve. On heater look at gpm flow under basic Information what is it?

 

[CuttyOX]

Pump next to the boiler top valve is almost closed. That valve should be used for flow control it's a shut off valve. On heater look at gpm flow under basic Information what is it?

Thats what I closed to get hot water

 

[Fitter30]

Turn the heating pump off see if u get dhw open the closed valve set flow at 4 gpm or less.

 

[CuttyOX]

@Fitter30 - The way I have been shutting off the circulation heating pump is by closing those valves (I do not know how to turn them off since they are hardwired). When the valves are open I have DHW for about 30 seconds before it gets cold and stays cold. And when I close the valves to the circulation pumps I then got hot water again.

 

[Fitter30]

Have a good chance of burning up the pump. Space thermostat turn it down? See if pump shut off. Heater pump does that run all the time? Your two pumps see that the.wiring is to the right.of the heater going to?