Brand new shower valve - hot water fades after a few seconds

[TomFOhio]

You need to shut those two valves off and then take your new cartridge out. Keep any faucets in that
bathroom closed off. Now, have someone turn on each valve one at a time and see if you get full
pressure on each one. Do the cold first and then the hot. Maybe stick a small towel in the wall under the
faucet body so you do make a mess in the wall.

 

[brassmookie]

Ok, did that and even with the cartridge out of the valve I still get the same behavior. Opening on the hot water shutoff, I get hot water for a few seconds and then it fades to cold.

 

[TomFOhio]

And thats with the cold valve being shut off, correct??

 

[brassmookie]

correct, cold is shut off, only hot open, and water goes from hot to cold in a few seconds

 

[TomFOhio]

Wow, it sounds like you have a cross connection somewhere in that line. Did you have any problems before like this
on your old faucet. Maybe see what all shuts off when those two valves are closed. No problem anywhere else in
the house.. Is your washing machine on this line.?? Maybe one the faucets that get shut off is bleeding through. We'll
go into more after you answer this.

 

[brassmookie]

Unfortunately I never used the shower prior to changing the valve. Just bought the house a few weeks ago and changed out the shower hardware before moving in. The only thing those two valves shut off is the bathroom sink, toilet and shower. No washing machine on the line. We get hot water to the bathroom and kitchen sink without any issues.

 

[brassmookie]

Update: I found the issue on another line. We have hookups for a slop sink in the basement as well (no sink currently installed). When I open the hot valve there, it does the same thing. Seems like it's just a problem when there is a large quantity of hot flowing through the system? Which is why the bathroom and kitchen sinks are working fine? Perhaps there is an issue with the mixing valve near the boiler? It does look a little corroded and seems to leak some. Photo attached.

 

[TomFOhio]

Do you have a regular water heater in the basement??

 

[TomFOhio]

Is there anyway you can cap that slop sink faucet off. That possibly could be the culprit

 

[Twowaxhack]

Replace the mixing valve. Consider installing a stand alone water heater.

 

[brassmookie]

Not sure what you mean by 'regular water heater.' We have a Burnham V8H boiler, no separate hot water tank. The slop sink hookups are always closed, since there is no sink currently installed. But are you saying we should close it in some other way?

 

[brassmookie]

Replace the mixing valve. Consider installing a stand alone water heater.

Seems like a good place to start. Does it seem strange that our boiler can't handle a shower though?

 

[Twowaxhack]

Seems like a good place to start. Does it seem strange that our boiler can't handle a shower though?

Could be the boiler not producing the gpm needed to operate the shower at the selected temp and volume. Try a restricted shower head.

Could be the mixing valve. Might just need adjusting.

 

[brassmookie]

Well... I had a plumber come by this morning and the solution was disappointingly simple. The minimum temperature on the boiler was set to 130. We upped it to 160 and the problem appears to be solved. Thanks to everyone for the input. Apologies for being a clueless new homeowner. Steep learning curve to all this!

 

[JeffreyWisc]

Well... I had a plumber come by this morning and the solution was disappointingly simple. The minimum temperature on the boiler was set to 130. We upped it to 160 and the problem appears to be solved. Thanks to everyone for the input. Apologies for being a clueless new homeowner. Steep learning curve to all this!

Hurts to pay a plumber to come out for something so simple, however hurts more to have them uncover some brutally time consuming solution! Glad you got it fixed, reading this, I could empathize!

Live and learn! Cheers!