DHW recirc woes on 10 story building

Timco

First a check valve that’s bad, alllowong tempering of DHW backwards through boiler and into hot line. This was an easy find. Question is with the pump running (26-99 on low speed 1”) it seems the pressure drop of DHW being used is greater than the pump force keeping the check open and thus closes the check against a running pump? How does that fly? Check is 5’ closer to 250 gal tank than pump.

Second issue. With pump off, cold makeup to tank stays cold. With pump on, it draws DHW back into cold supply line. Heats right up every time. There MUST be a X connection in a unit?

The cold hard, cold soft, hot and recirc just run past each lobby straight up to the top. 2”. The recirc is 1”. Each unit has a loop from hot to recirc within their ceiling.

Timco

Zman

I sounds like you have a typical recirc setup. The circulator just pulls hot water from the far units back to the inlet side of the tank where it can be reheated. The flow stays essentially the same, it just moves water around in a big loop.

What are the complaints that brought you to this job? Is it a cold/hot cross connect in part of the building? Those are usually issues in the building like add on shower accessories with valves on the head or janitor sinks with "Y" connections.

A cross connection in the building can appear like a cross connection in the mech room, especially with a pump assist. If water is pulled through the cold side of the shower valve on the top floor, that water needs to be replaced by water in the mech room. It is going to have to come from the recirc. This puts hot in cold side.

A check on the cold feed upstream of the tie in might fix the symptom but not the underlying problem. The folks on the 10th floor unit will never believe that their fancy new hand held shower head is causing all these problems.

JUGHNE

The janitor/mop sink has been always my first suspect.
Chemical dispensers are installed and connected to the hose bib faucet. They are supposed to leave only the hot valve turned on as they want water to the dispenser on at all times so cleaners has to just push one button and the mix is made.

Most people do not understand the cross connection problem.
Flush valves WC's sometimes flush with hot water.
Often the cold faucet handle is removed to prevent the cross.

hot_rod

Is there a valve on the DHW supply from the tank that is partially closed? Really on reason for DHW to want to go out the recirc instead of the 2" HW supply.

Is there a 3 way mix valve in the system? Weird things can happen with recirc and thermostatic mix valves if not piped properly.

A new problem, or always been going on?

Timco

Ok. Update. Swapped the bad check valve at the recirc termination. Got recirc back on. Most floors are fine. 2nd floor. If I let hot water run long enough, it’s system hot. Shut hot off for 1 minute and it’s primed cold. City cold. Then if left on long enough hot comes back full temp. On the 7th floor, the cold side is being primed hot. If left running, it gets cold. In the mechanical room, the recirc line is almost tank hot when pump is left on high. Not tempered at all. No valves are partially closed. I’ll have to check janitors room tomorrow for one of those Y connectors. I’ve seen that before where half a 4-plex was warm at best and half was fine. This is a real stumper. Throughout the building there’s less hot pressure but I’m sure there’s some rust obstruction past the tank because cold can be 80lbs and tank gauge says 95lbs. It doesn’t drop at the same rate. But this is a 2” line that can be partially blocked anywhere and it’s been that way for a long time. This all started happening within the last 2 days. No major work or remodeling was done.

Timco

I even bypassed the softener to make sure it wasn’t the source of the hot side pressure deficiency. Tank is fed from the softener.

Timco

Zman said:

I sounds like you have a typical recirc setup. The circulator just pulls hot water from the far units back to the inlet side of the tank where it can be reheated. The flow stays essentially the same, it just moves water around in a big loop.

What are the complaints that brought you to this job? Is it a cold/hot cross connect in part of the building? Those are usually issues in the building like add on shower accessories with valves on the head or janitor sinks with "Y" connections.

A cross connection in the building can appear like a cross connection in the mech room, especially with a pump assist. If water is pulled through the cold side of the shower valve on the top floor, that water needs to be replaced by water in the mech room. It is going to have to come from the recirc. This puts hot in cold side.

A check on the cold feed upstream of the tie in might fix the symptom but not the underlying problem. The folks on the 10th floor unit will never believe that their fancy new hand held shower head is causing all these problems.

10th floor was remodeled new about 5 years ago. No changes recently. All new fixtures. No changes.

Timco

JUGHNE said:

The janitor/mop sink has been always my first suspect.
Chemical dispensers are installed and connected to the hose bib faucet. They are supposed to leave only the hot valve turned on as they want water to the dispenser on at all times so cleaners has to just push one button and the mix is made.

Most people do not understand the cross connection problem.
Flush valves WC's sometimes flush with hot water.
Often the cold faucet handle is removed to prevent the cross.

No chemical feed but I’ll look for any Y connector. Doubt there’s one in there but I’ll look.

Timco

hot rod_7 said:

Is there a valve on the DHW supply from the tank that is partially closed? Really on reason for DHW to want to go out the recirc instead of the 2" HW supply.

Is there a 3 way mix valve in the system? Weird things can happen with recirc and thermostatic mix valves if not piped properly.

A new problem, or always been going on?

New problem, last 2 days. No 3-way valves at all. All lines open. There is a restriction on the 2” hot and that’s why when allowed it was making up for the restrictions via the recirc. Now with working check it’s back to just less flow on the hot side.

hot_rod

Is there a 3 way thermostatic valve?

Timco

hot rod_7 said:

Is there a 3 way thermostatic valve?

No sir.

Zman

This has to be a cross connect. Are the units independently owned? One of these with a valve on the handle can cause this.

https://www.amazon.com/Delta-7-Spray-Shower-Chrome-75700/dp/B000LV7VXW/ref=sr_1_20?ie=UTF8&qid=1543200418&sr=8-20&keywords=hand-held+shower

Timco

Zman said:

This has to be a cross connect. Are the units independently owned? One of these with a valve on the handle can cause this.

https://www.amazon.com/Delta-7-Spray-Shower-Chrome-75700/dp/B000LV7VXW/ref=sr_1_20?ie=UTF8&qid=1543200418&sr=8-20&keywords=hand-held+shower

All independently owned. I’ll ask.

Timco

So, 80psi on cold service and 110 at tank. The restrictions in the DHW delivery line are too great to allow DHW to the 9th or 10th floors while anyone else is using water. There you go. Obstruction is post tank. Checked every single unit and sink. No X connections.