I am at my wits end, I am in so way skilled in plumbing so any help is appreciated. My upstairs shower/bath for the past month or so had been acting up, it is a delta unit (judging by pictures on the web I think it is a 600 series) single knob that goes left for hot, right for cold, and up for pressure, when I turn on the shower and get to comfortable temperature it will gradually get cold after 1-2 minutes. it gradually gets cold and then it is FREEZING, if I cut off the water and cut it back on, same thing, fine for a minute or two then gradually gets ice cold. The problem is only in the shower and not the bath faucet, or any other showers in the house. I called a plumber and he said he did not think it was the valve and we both noticed that when the shower handle was not pushed all the way up the problem happened, but when it was all the way up it did not. that was a week ago and I can confirm that it is happening no matter the pressure. also it does not happen everytime, for example, this morning it happened to me but my wife showered two hours later and it was fine. Sorry for the novel but I wanted to put every bit of information in here that I could think of. Thank you in advance.

just to confirm.. when the shower turns cold, if you leave it running cold and open another faucet is that hot ?
trying to eliminate a hot water tank/tankless or shower valve crossover problem..

Yes, any other faucet in the house is fine, it seems to be isolated to just this particular shower.

Also, if you hit the button for the water to go to the bath faucet it is fine, no temperature change there.

well then you need to definately identify which delta valve you have and contact delta for free advice and free replacement parts.

Can I assume you have a circulation system with a pump at the heater.

Contacted Delta and they advised to flush the faucet, so I did that to no avail, it happened to me this morning when I let the shower run for a few minutes, I also checked the faucet upstairs and while the shower was acting up so was the faucet, and yes I do have an "ECU" unit installed under the house, it looks like it was installed in this last 5 years or so but im not certain, we have only lived in the house for two years. I have tried to get the elements out but they will not budge, I have bought the socket for them from HD and would not work, I have also bought two sockets, a twelve point and a six but the lip on the element is too short and the socket would just roll off.

What is an ECU unit? is it a water heater or a circulation pump? If it is a water heater, your symptoms do not indicate it is faulty.

ECU heater is some sort of heat pump system..
[www.webrepshvac.com]

at this point there are too many possible sources of this problem to try to figure out over the internet.
1) crossover at the shower valve ?
2) problem with a recirculating pipe ?
3) problem with the electric water heater such as element, thermostat or dip tube ?
so for now, i would suggest you contact delta for replacement guts for the shower valve. it may not be the problem but it is a good place to start. if that does no good then get a pro to come out and start troubleshooting.

Will do, and just an FYI, it is 9:20am right now, it happened to me at 6:45am and just got off the phone with the wife, worked fine for her at 8:45am. So confused.....

"Do not return the Heat Recovery Unit’s hot water by placing a Tee in the
hot water delivery pipe above the water heater. This approach will allow
water to pass directly from the Heat Recovery Unit into the Home; and that
is likely to create bursts of cold water in the shower when the Heat
Recovery Unit cycles on while the shower is running.
• Do not return the Heat Recovery Unit hot water by modifying the water
heater’s pressure relief valve opening."


I just read this on the link you posted packy, and I can confirm that the return line from the ECU unit does come back to a tee above the water heater, do you think I can kill power to that unit to trouble shoot or bypass it all together or will there be a problem?



Edited 1 times.

i don't have much experience with this type unit. so i will defer to someone who does.
i do know that the electric water heater should be the type that has extra tappings on the side.
of course this type costs somewhat more than a regular electric tank so to cut corners someone used a tank without the proper tappings and installed a tee in the wrong location.
as i said i'm not too good on this but i believe this picture will get the point across.
i know it is solar but the principle is the same..
[www.apricus.com]
see picture at the bottom..
The water is drawn directly from the bottom of the tank, through the collector and returned to a position about 1/4 the height of the tank



Edited 2 times.

This unit works differently. The cold comes off a tee in the cold feed, but returns the hot water to the drain valve. It specifically says NOT to use any side tappings or a tee in the hot water line as a return point. From their description it appears that if the unit is operating and it was connected improperly, they CAN get cold spurts. It may be that she showers when the AC is turned off.

i understand but he posted quote..
"I just read this on the link you posted packy, and I can confirm that the return line from the ECU unit does come back to a tee above the water heater"...

Yes that is surely my problem, the only thing I don't get, is why is it happening now after 2.5 years of living here??? I can't really find anything online so I may take a chance and cut the copper lines and cap them.

And THEY state that doing so CAN cause his symptoms.