Our main shower is not for 30 seconds and then stays cold. Sometimes warms up a.bit but not for long. Sink is hot and other shower has not water. The main shower has scald guard on single lever.

Oil company thinks mixer at boiler is bad but why is all other water warm or hot.

when the main shower is running and it's water is running cold, what happens at the SAME time to other faucets?
if the shower is cold but at that exact time others are hot, the shower has a problem.

What brand of showervalve do you have? How old is the shower valve and when was the last time it was serviced? And by who?


Best Wishes

Check the anti-scald settings on the shower faucet first before going after the mixing valve.

We have delta guard scald. I will take a picture as it was here before moved in 8 years ago. Can't even figure out how to adjust.
I turned shower and sink on. Very not for 30 secs and then colder, then remains cold. Sink gets colder but stays warm. At this point figure used up much of hot water as small tank. Kept sink running with shower on. Sink never returned to very hot but warm. Once turn shower and sink off then turned sink back on after 1 minute, sink very hot.

Sorry for ignorance but when you say valve you do mean knob to turn water on, correct. It's a single round knob with rectangular plate that says scald guard

you have a tankless coil in the boiler that has lost it's efficiency.
this is a common problem. discus the possible solutions with your oil company.
they can run a chemical thru the coil to help it transfer the heat better.
they can replace the coil
they can add a storage tank
or they can install an indirect water heater.

The Scaldguard has a balancing spool in the body to the right of the valve assembly, and it is probably broken or stuck, but either way you should replace it. You have to remove the large trim plate to access it, and sometimes it can be a challenge to remove it.

oil company said coil was good just the mixing valve. hard to believe coil since pipes from boiler is too hot to touch, just water to shower. here's a pic of the delta guard. looks different from delta's site when i tried to figure out how to adjust.

[s841.photobucket.com]

if the water in the sink is also cold at the same time the shower is cold, it is the coil..
it is a pretty simple task to turn on the shower and the sink and then feel the pipe leaving the tempering valve at the boiler.

Hi. The sink water was warm when both on. However after a minute of both off and then turning sink on only sink water was hot and stayed warmer then prior while on. If I have shower only then stays much cooler.

Posted pic of showered valve but no idea what I'm looking at

a tankless water heater is rated in gallons per minute (GPM).
a faucet does not deliver the same capacity as a shower. so, it is possible to exceed the GPM of a failing tankless by running a shower with a generous shower head but almost impossible to exceed the GPM with a faucet alone.
it is also possible that the shower mixer is bypassing cold into hot and causing your problem.
turn on the sink hot and feel the pipe marked (mix) at the tempering valve which is located right at the water heater. it should be nice and hot. have someone open the shower to full hot. feel that same pipe. if it cools down within seconds of the shower being turned on, the tankless is losing efficiency.
your tempering valve should look something like this depending on what brand it is.




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Just curious.....Are you on a well?

No well. Was told coils are good and other shower is ok. Few months ago plumber took a plastic piece off from shower head for stronger flow. I think it all got worse since then

An "immersion coil" can be "good" and still not heat the water properly as it flows through, IF the fins on the outside of the coil have become 'clogged' with sediment. We used to have to remove the coils and wash them off periodically.

So should I call oil company back to check coil or should I replace shower head and valve or just try and figure out how to replace cartridge. But again I would assume if bad coil then we wouldn't get much not water elsewhere in house

Tx all

He removed the flow restrictor. You now exceed the gpm the coil is capable of heating. Go buy a good shower head, and leave the flow restrictor in it.Your boilers tankless coil is rated for so many gpm at a certain temperature rise. By removing the restrictor the water is traveling too fast through the coil to be heated properly.If the boiler has been in service for a while, you may have also lost some of its ability to transfer heat because of mineral buildup inside the coil. Often a side-saddle tank(storage) can be added to the system to help alleviate shortage issues.



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Thanks. Might sound sill but do I just buy shower head or has to be valve as well

The showerhead is all you need. There are ones that change patterns while the shower is running, to trick you into thinking you're in the carwash.

quote; But again I would assume if bad coil then we wouldn't get much not water elsewhere in house

Bad assumption, unless you have another shower which does not have that problem, because a tub or shower uses more water faster than anything else. No use replacing the valve until you know the problem, otherwise you will spend a lot of time and money, but still have the same problem.

Nj,

We have two showers. The one that I'm having problems with ands gets cold and stays cold or less then lukewarm. The other shower on same floor stays warm, gets cold but gets warm again in a few minutes.