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 low hot water pressure at shower valve
Author: Sterling (Non-US)

My 8-year old single handle shower valve had lower pressure on the hot vs cold. It had also started making a loud shrieking noise when left on full hot (like when re-warming a cool tub). I replaced the cartridge (HK40) and so far the noise is gone but the lower hot pressure remains. The temp setting on the cartridge is at the highest setting on the "+" side. The pressure is fine on all other fixtures in the house. When I changed the cartridge I turned the stop screws in and out a few times in case there was some kind of calcium build-up but that didn't change anything.

As I'm typing this I'm wondering if the high temp setting on the cartridge is actually making the valve reduce the hot water too much? I'm not sure exactly how that mechanism works.

Any ideas on why the hot pressure might be low?

EDIT: After some more testing the shrieking noise has returned when on full hot. So the new cartridge has done nothing.

Edited 1 times.

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 Re: low hot water pressure at shower valve
Author: packy (MA)

did you flush the valve with the cartridge removed?

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 Re: low hot water pressure at shower valve
Author: Sterling (Non-US)

No I did not. The cartridge is quite easy to get to so I could try it.

After some more troubleshooting I'm thinking the issue is with the diverter. When I get the valve to start shrieking it stops when pushing the button and sending the flow to the shower head. It only makes the noise when hot water is coming from the tub spout. While moving the diverter button in and out I did see some water leaking out of where the button/knob is. The leak stops when either all in or all out. Would the diverter cause the low hot water pressure?

If the diverter is in fact the issue, the next problem is getting to it. It is controlled with a button right above the single handle. The knob just turns endlessly. I remember it was fiddly when it was installed and would only screw on while pressing it in hard against the spring. I have tried to unscrew it while pressing it in and while pulling it out but I'm guessing that mineral deposits have fused it to the shaft and the whole assembly is turning. The next problem is that it is an Uberhaus brand (house brand of Rona/Lowes in Canada) and parts are hard to find easily. I found the cartridge on Amazon after finding a parts diagram online and matching the part numbers. I am hoping that the diverter assembly is generic like the cartridge. I will include a photo and the diagram below.



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 Thanks so much thumbs clap
Author: Sterling (Non-US)

Packy you're a champ! Your flushing suggestion was right on the money!

Thanks so much for pointing me in the right direction.

So for any others with the same issue here's what I did: I have ball valves for the shower supply accessible in a closet behind the tub. I shut the water off there. I removed the cartridge. Then I slowly opened the cold ball valve. (Just as a practical note to any other schmucks doing this job alone - the wind created by the water jet blasting out of the valve body will drag a shower curtain inward so that it does nothing to keep water from getting all over the bathroom).

Then I did the same thing with the hot. I immediately heard the familiar squeal which was then replaced by what sounded like a 2 second machine gun burst about every 10 seconds which I could feel severely vibrating the supply pipe. The flow was also obviously lower on the hot side. I opened and closed the ball valve repeatedly to try and dislodge whatever night be impeding the flow. Then I opened and closed the stops on the valve body and released the water at different amounts ranging from barely open to open full. After messing around with the stops for about 20 minutes I noticed that the spray seemed the same from the hot and cold sides. I also noticed bits of debris in my bathtub. I replaced the cartridge and handle and hot water pressure was back! I ran it continuously on hot for about 20 minutes and the flow stayed the same and there was no noise.

Edited 1 times.

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 Re: low hot water pressure at shower valve
Author: packy (MA)

glad you were successful.

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