HW to fixtures is intermittent

Having an issue with some older second floor domestic HW lines. From time to time, the DHW at the second floor fixtures goes cold or 'luke'-warm. It does not recover by leaving the tap open and running the water hot. The temporary "fix" to the problem has been to go down into the basement, and open the hot tap of the utility sink, which immediately runs hot water (the domestic tank is all of 25' across the basement.) As soon as we have done this, the 2nd floor taps quickly (under 1 minute) go back from cold to Hot.

Background on the house DHW piping:

* From DHW tank to utility sink = 1/2" Cu, roughly 25' horizontal
* From basement branch to 2nd floor = 1/2" Cu
* HW fixtures on 2nd floor branch line include:
- (2) sinks
- (1) dishwasher
- (1) shower

Would really appreciate any insight as to how come this happens. Would it be a problem with air getting into the system somehow?

Will Kessler
Portland, Maine

sounds like a crossed water condition

when did it start? who has done what ? and where ?

do you have a hot waterr circulating line

Hi Frodo:
thanks for writing...not sure when it started, we've always been patient with the HW lag times in the house, which just has the 1/2 cu lines coming up 50-70' from basement tank. I can't imagine that a plumber would have connected the hot to the cold en route to a fixture. At least I can say is that each time I've made a change to the plumbing -- added a branch for second W/D in basement, added a hot branch / valve for a dishwasher, I've been darn sure which was which.

Attached is a sketch of the layout that I was able to visually confirm this morning. The fixture at the far right of the drawing are the 2nd floor ones where the problem occurs.
Will

View attachment DHW lines sketch.pdf

Willis18, many of our members are a little gun shy about opening up .pdf files. Can you use a different avenue to display pictures for us?

No problem. you can also use the URL-view linked through drive. let me know if unable to open it:

https://drive.google.com/file/d/0B5blaaabvk6VNzZtUWh6UXc5dEU/view?usp=sharing

clunk..........

clank........

Clackity clack


Does that heater provide heat for space heating as well?
If not why do you have a tempering valve.
That could be the malfunction.
It can be allowing more cold to mix with the hot.

Why the running the of utility sink fixes it is a mystery.
Possibly due to how the cold supply to the other group of fixtures is connected in close proximity to the tempering valve.
I would start by replacing the tempering valve and install an isolation valve to cold supply to the tempering valve. if the problem persists turn off the cold supply to tempering valve temporarily to see what happens.

you dont have temp gauges on both sides of the temp valve ?

Mr_David said:

Clackity clack


Does that heater provide heat for space heating as well?
If not why do you have a tempering valve.
That could be the malfunction.
It can be allowing more cold to mix with the hot.

Why the running the of utility sink fixes it is a mystery.
Possibly due to how the cold supply to the other group of fixtures is connected in close proximity to the tempering valve.
I would start by replacing the tempering valve and install an isolation valve to cold supply to the tempering valve. if the problem persists turn off the cold supply to tempering valve temporarily to see what happens.

Click to expand...

Hey Mister David, the DHW and heating systems are separate. the tempering valve is there for safety, since at times the DHW tank can get quite hot.

My observation is that the DHW lines to the utility sink (in basement), to the washer (in basement), and 1st floor fixtures (up 10') have no issues-- water there is super hot. They are all downstream of the mixing valve, and are all 1/2" lines. BUT they are also much closer to and at lesser height above the hot water feed. I guess we could change out the valve just to see (@ 100-130 bucks). but it's funny that none of the other taps are having the issue.

The thermostatic mixing valve was the culprit. Changed it out, and problem solved.

I hope you installed temp gauges on both sides of the mixing valve so you can see a problem next time