On demand WH problem.

jhilly

This only happen with shower all other fixtures are fine.  5 minutes into show it goes cold. .close to 5 minutes of cold hot water comes back.  
Well putting out over 10 gallons per minute.  Into 20gal expansion tank.  3/4 lines to shower reduced to 1/2 at fixture. Distance is 6 feet.  Kitchen faucet 40 feet never lose hot water.

Jamie Hall

Well for starters, a 10 gpm well pump into an expansion tank with 20 gallon capacity isn't going to last long. You're murdering your well pump. You should -- at the very least -- have a 75 gallon tank (Well-X-Trol 255).

Jon_blaney

If it only happens with the shower them the shower is the problem. Shower valve has intemittent issue.

hot_rod

Do you have a tankless water heater.

jhilly

Jamie Hall said:

Well for starters, a 10 gpm well pump into an expansion tank with 20 gallon capacity isn't going to last long. You're murdering your well pump. You should -- at the very least -- have a 75 gallon tank (Well-X-Trol 255).

Do I even need a pressure tank with tankless hot water? I have a shared well.  Pressure tank at pump for both users might need a change?

jhilly

hot_rod said:

Do you have a tankless water heater.

Yes

Jamie Hall

You only need an expansion tank for the hot water if there is a check valve (or pressure reducing valve) between the hot water heater and either a public supply or a well with its own expansion tank. Now in your case it appears that there is a well which has an expansion tank for well pump control, and I assumed that you were referring to that tank when you said 20 gallon capacity.

Well pump control tanks are usually sized on the basis of the well pump capacity and the pressure swing which is allowed (Note that there are exceptions to this! There are a number of varieties of on-demand boosters and pressure pumps which don't use pump control tanks as such -- but which do need, in exchange, a smaller pressure tank for hot water... ). What is the actual size of the pressure tank for the well?

Larry Weingarten

Hi, What is the gpm flow of the shower head? If hot flow goes too low, the tankless can shut off. I know some folks who run a sink faucet when showering so their tankless keeps working. It’s a waste, but could help identify the problem.

Yours, Larry

hot_rod

You need to have someone stand by the heater and observe what happens during the shower 

It sounds like it kicks off under some flow conditions

Have the screens been cleaned, most have strainers on the inlet connection. A lo flow, generally .35 or .50 flow switch is in the piping somewhere, it could have an intermittent failure preventing the unit from firing.  Could be a temperature high limit shutting it down. 

The manual should explain some of the troubleshooting steps and routine maintenance required

If the shower keeps flowing at a somewhat steady rate, and pressure, shouldn’t have anything to do with the well

jhilly

So if there is a tank at the pump, there is no need for a tank in my house?

Jamie Hall

jhilly said:

So if there is a tank at the pump, there is no need for a tank in my house?

Probably. The essential point is this; is there a check valve or pressure reducing valve between the hot water heater and the well control pressure tank? If there isn't, you're fine. If there is, you have to have small tank on the hot water.

jhilly

Well as it goes I had to high of a flow rate.  Dialed back the valve and it seems to have solved my issue.  Thanks to all for the aid!