Ask Me Help Desk - Rheem RTG-54PVN - no hot water pressure to the tub

Hello,

I installed a Rheem RTG-53 tankless... I have all of the required pipe sizes (3/4" copper & gas)... I have a Kohler bath faucet (hot/cold is a single-handle control)... I have a 1100 sq ft ranch home, with one bathroom...

I am lucky if I get up to 50 degrees in my tub/shower... The odd thing is, I had good temperature when the 40 gallon tank water heater was in use just yesterday.

My problem seems to be a hot water pressure issue to the tub only... The sink in the bathroom has separate hot and cold handles... and when I turn on the hot, I get the same pressure that I did with the tank water heater...

But when I turn on the bath faucet, the cold water is overwhelming the Hot...

I took apart the bath faucet and inspected the impeller looking things (dont know what they are called) and they look OK and they turn freely... So, out of curiosity, I installed shut off valves on the lines to the tub & turned off the cold... the hot water started flowing when the tankless heater kicked on & the water coming out was 120 degrees, but the pressure was fairly weak...

Now, taking showers with the cold water to the tub turned almost all the way off, we are able to take showers, but this AM, the water went cold while in the shower... I could turn off the faucet, wait a minute and turn it back on & the water would get hot again. So, it would seem to me that the flow to the tub is restricted somewhere, somehow, and the flow through the water heater isn't enough so it turned off (safety feature)...

So, would you guys say that I most likely have debris in the line? Or is it possible that the water heater is restricting flow? The water heater is capable of heating up to 5.3 gallons per minute, so I would think that the water heater isn't restricting flow...

If I do have blockage, what it the best way to try to clear it?

Help!

Barry
Milwaukee, WI

The best way to clear a faucet of debris is to open up the faucet and turn the water back on to flush out the valve body and supplies. This sounds like the problem's in the Kohler bath faucet. I really need the model number of your faucet but here's a exploded view of a temperature control Kohler, Does it =look anhything like yours? (see image) and tell me more about thuose"impellers" Can you see them in the drawing I put up? Regards, tom

Quote:

Originally Posted by speedball1

The best way to clear a faucet of debris is to open up the faucet and turn the water back on to flush out the valve body and supplies. This sounds like the problem's in the Kohler bath faucet. I really need the model number of your faucet but here's a exploded view of a temperature control Kohler, Does it =look anhything like yours? (see image) and tell me more about thuose"impellers" Can you see them in the drawing I put up? Regards, tom

Tom,

The drawing looks kind of similar in the upper right had corner... the "plungers" that they refer to look similar to the "impellers" that mine has... I can take a picture & post it on my next reply when I get home...

It is a Nieidecken faucet! I just found it by seaching Plumbing Parts Depot,Faucet Parts,Toilet Parts,faucet repair parts,toilet repair parts,ppd1.biz!

http://www.plumbingpartsdepot.com/kohlernieidecken.pdf

I have also attached a pdf of what my plumbing looks like...

That makes sense that the tub fixture may be the cause... it is just hard to fathom, as with my old tank water heater, things were fine...

Thanks for your help!

Barry

Did you open up the valve and flush out the supplies and valve body as I suggested? Let me know, Tom

Quote:

Originally Posted by speedball1

Did you open up the valve and flush out the supplies and valve body as I suggested? Let me know, Tom

Well.. when I had the hot water line cut to add a shut off valve on the tub, I tried to blow out the faucet, using a rubber tube stuck into the hole where the plunger goes... Either I don't have enough PSI in my lungs, or the blockage isn't in that part of the faucet, because the low pressure still exists...

I will try your suggestion when I get home... did you mean, shut off the main, open my lowest faucet to drain the lines, then close the lowest faucet, turn back on the main, & then turn on the faucet in the tub? That way, air would be forced through the lines and out the tub spout?

Ok... I tried flushing the lines & the valve... I still have low hot water pressure. I am starting to really regret my decision to purchase a tankless heater.

I wanted to try to gauge how fast (or slow in my case) the water was coming out... With the thermostat set at 114 degrees, I grabbed a gallon milk jug and timed how long to fill it. It took 17.6 seconds... That works out to be 3.4 gallons per minute (if I calculated right)...

Looking a little closer at the documentation, I saw that the max flow rate for my model is 3.4 gallons per minute if I need to raise the cold water up 70 degrees.. my incoming water temp is 44.6 degrees.

So, the poor water pressure is probably by design.

If that is indeed the case, when summer rolls around & the cold water temperature in my house rises, my water pressure should increase as well.

Does that seem right to you?

Quote:

when I had the hot water line cut to add a shut off valve on the tub, I tried to blow out the faucet, using a rubber tube stuck into the hole where the plunger goes... Either I don't have enough PSI in my lungs, or the blockage isn't in that part of the faucet, because the low pressure still exists...

You don't blow any trash back into the supplies, you turn the water back on and flush them out.

Quote:

I tried flushing the lines & the valve... I still have low hot water pressure.

The pressure was the same coming out of the open valve body? No increase?

Quote:

So, the poor water pressure is probably by design. (so it would seem)
If that is indeed the case, when summer rolls around & the cold water temperature in my house rises, my water pressure should increase as well.
Does that seem right to you?

As the ground temperature raises so will the ambient temperature of the water in your water service. Sure sounds right to me.
Regards, tom

Quote:

Originally Posted by speedball1

you don't blow any trash back into the supplies, you turn the water back on and flush them out.
The pressure was the same coming out of the open valve body? No increase?

as the ground temperature raises so will the ambient temperature of the water in your water service. Sure sounds right to me.
Regards, tom

Thanks very much for your input. It is great that you are here for us novice plumbers!

I am a bit disappointed that the documentation for Rheem Tankless Water Heaters didn't explain things better.. For instance, I didn't know what the average shower output was, 3, 4, 5 gallons per minute?

Also, I found a different manufacturer (Powerstar) that shows a map of the US & tells you which model you should buy based on geographic location:

Powerstar electric tankless water heaters whole home instantaneous point of use

I wish that I would have seen that before I took the plunge.. or maybe I should have simply bought the RTG-74PVN model for more heating power for a little more $$.

Thanks again!

Barry

You are probably correct. You could have used a larger unit, however, you still might maintain temperature by installing a water saver shower head. This will cut down on the volume of water used and lessen the 3,4 gallon draw.
God luck, Tom