Low shower pressure-hot water only-1 shower only

[mindfrost82]

I have one shower/bath that has low water pressure with hot water only.

It has a single knob Kohler valve on it. We can turn it almost 90% and the water pressure is fine, but once we turn it the last 10% it drops by probably more than half.

When we pull the knob on the bath faucet to turn the shower on it'll make some noises and turn on. Its less noticeable through the shower than the bath faucet, but there is still a little less pressure.

We also don't have the range of hot water we used to have. It seems like the hot water is only within that last 10% of the knob and if we try to go below that it'll get cold.

I've read about clogged/dirty cartridges on this site and others, but since I don't really know what I'm doing I would like someone to walk me through how to get to it and see if that's the problem.

Or could it just need adjusting for the hot water? Within the first year of moving in they had to come out and adjust that shower because the hot water kept going away in that shower, so they adjusted the knob and the temp on our water heater.

We have a Rinnai Tankless Water Heater and no water softener. The house is about 2 1/2 years old.

Any help is appreciated.

[jadnashua]

Some tankless units are set up with flow restrictors on them to try to maintain the temperature rise...you may be hitting the max flow to keep the outlet water hot.

If you have hard water and haven't delimed the unit, its ability to produce hot water will be diminished, too. These things take more maintenance than a tank type heater - not saying you shouldn't service them too, it's just that you'll notice problems much faster with a tankless if you neglect it.

[mindfrost82]

Thanks for the info. I need to get the tankless serviced soon since its never been done.

I'm still thinking its something with the one shower though. I have another identical shower/bath that works fine.

[jadnashua]

There could be some crud caught in the inlet to the valve. Some of them have a filter screen on the inlet. Also, you could have in-line shutoff valves, and the hot might not actually be fully opened. The pressure balance valve could be sticking.