Leak at cold water inlet of direct hwh

Steve M_2

Thought I'd chime in on mixing valves. Back in my solar days, we'd install Watts 70A mixing valves on water heaters to temper the solar preheat temps which could be 160 plus. Watt's and Taco both recommend a check valve on the cold line going to the valve to prevent thermosipioning back up the cold supply.

I once tried trapping the hot line coming out of the tank before the mixing valve and a customer complained that it took a long time to get a constant temp. When hot water is turned on the cool water in the trap hits the mixing valve and then the blast of hot water reaches it and it seems to take awhile for the thermostat to adjust. So I kept piping the hot of the mixing valve right out of the hot outlet so the valve see's constant hot temps so in my mind, less time to react. I see more elememt failure from mineral and scale build up. I tell customers once every couple months to run hot water and exercise the valve by turning it back and fort to loosen up the crud and return it to the proper position. The Taco valve seems to be superior to the Watt's valves so far.

Ok, there's my long winded explanation on what I know about mixing valves.

Steve M.

D107

Newly installed gas-fired American Pro-Line 50 gal 40k btu

I'm assuming installer (a good plumber) can easily repair this, but noticed the little 'cup' the cold water pipe goes into is filling up --from below--and overflowing slightly--no real 'flow' but obviously it shouldn't be leaking. Working fine otherwise. Has a Taco 5000 mix valve installed; tank temp is set for 140, mixing down to 120. This temp shouldn't create too much pressure should it? (see photos)

Any ideas?

Thanks,

David

Glenn Sossin_2

Find the leak

A little trick I was taught - Dry everythin as best you can, than spray talcum powder in the leak area. You will see the exact source of the leak within a a few seconds as the talc will change color and no longer be white. Then you know what to tell your plumber when you call him back to fix it.

You appear to be missing a thermal expansion tank. That could result in very high pressures 100psi + and be the contributing factor to the leak. You should seriously consider adding this tank. If you don't, you may come home to a wet basement one day.

D107

Thanks; never heard of expansion tank on a direct hwh....

but I learn new things on the wall all the time. The water main has no backflow preventer. The leak does not appear to be from any of the plumber's sweat joints. The leak seems to be coming from below the top of the tank.

Plumber is on his way......

Thanks,

David

D107

plumber had complained that some mixing valves on direct hwh

had callbacks for no hot water. So I wondered if the photos showed any piping problems.

Thanks,

David

D107

closer piping details

see attached photo

Unknown

Good valve

the only issue I ever had with this location is element failure as the water is hottest at the top of the tank. I usually "trap" them.
As far as the leak goes, it could be a "bum" dip-tube nipple thread, or bad weld on the tank "boss". It happens.

Dave

D107

thanks, yes it's also next to flue.....

Don't know if this applies but directions say: 'in applications where hot water thermal syphonage is a concern the valve should be trapped installing the valve below the cold water inlet to the heater. in installations where the valve is supplied with unbalanced hot and cold pressures greater than a 5 to 1 ratio please consult the factory.'

thanks,

David

Joe Mattiello

Hi David
After reviewing the pictures you sent, I’m trying to determine how you think the 5000 series mixing valve installed on the hotside, is leaking over the cold water supply where it enters the water heater. If the valve was leaking I would help you with a repair kit. let me know If I can help you.

D107

thanks joe--I guess I didn't make it clear

that the valve wasn't leaking, just the steel nipple going into cold inlet--which has now been tightened.

In the process of looking at the overall piping I was advised that the location of the untrapped 5000 might be subject in the future to element failure (from rising heat). I wouldn't have thought of this, except the installer had mentioned having trouble with a number of the valves in the past, and I wanted to nip that potential problem in the bud if the piping was an issue. Valve is working fine, as is the one installed on the family's Buderus ST-150 last year.

Many plumbers have told me they never install mixing valves on indirects--most customers don't want to pay for it. Taco has some pretty explicit install directions which I'm sure not every installer follows. I think it's great anti-scald protection plus it must boost the hot water capacity of a 50 gal boiler (140 deg down to 120) significantly.

Thanks,

David

Joe Mattiello

I looked at the installation, and it is fine.

D107

as usual this has become a learning experience...

Thanks Steve. As you can see from the piping photo there is no check valve, no trap (I know not all situations require the latter) and there is no 8-12" clearance on the incoming cold line before the cutoff to the cold feed to the mixing valve as the TACO diagram recommends.

Valve is working but overall hot water pressure is low, which I'll try to raise from the PRV at the main. The addition of the mixing valve does add quite a few ELs and pressure drop so I guess that's to be expected. Of course it may not help that all the 2nd floor piping risers and branches --where the shower is--are reduced to half-inch from the 3/4" on the ground floor. But I'm not a plumber I don't know.

David