I recently installed an inline water heater. It's not a high-end
brand, Eco-Temp or something like that, we needed a new water heater
and this one was priced similar to a 40-gallon tank heater, so we got
it. It runs on propane (we do not have natural gas).

the intensity of the burner does not adjust adequately based on flow
rate. If you turn the hot on full blast, the water is passing through
the flames much more quickly, and doesn't heat up as much. If you
turn on the hot water only a little, it passes through the flames much
more slowly and you get much hotter water.

It sounds like your tankless water heater is undersized for your
situation.

Tankless heaters are generally rated for a given temperature rise at a
given flow rate. If you draw water faster than it can heat it, you'll get
cooler water.

Likewise, if the water coming into your home is colder, the outgoing
water will be colder too. The heater can only raise the temperature so
much.

It would be like trying to heat an entire house with a small space
heater. If you close the doors you might be able to heat one room. Open
the doors and you'll lose heat faster than the heater can warm it.

When you bought your heater you should have checked the temperature of
your water supply, what flow rate you would need (how many fixtures you
would be running at once), and selected a heater that could meet those
requirements.

At this point, you really only have a few options.

1. Return the tankless heater and go back to a tank heater.

2. Replace the tankless heater with a more powerful model.

3. Add a valve to the water line to reduce the flow rate (giving the
heater more time to heat up the water).

Of course, putting low flow aerators on all of your fixtures would help
too.

One way you can test if your water heater is the culprit is to open a hot
water valve at a sink or washing machine outlet. Basically someplace with
the "two handle" operation you are describing. If the water cools down as
you open the faucet further, you know the heater isn't able to keep up.

I'm ****ed as hell at these bull**** "scald safe" faucets in my home.

As far as I know, single handle pressure balanced shower faucets are now
required for new construction (or remodels when you upgrade the
plumbing).

You might try replacing the balancing valve in the faucet, it might just
be defective. Sometimes they get plugged up with grit and stop moving
correctly.

half the faucets in my house, the set screws were so crusty/rusted
I either couldn't turn them or broke something trying to get them
loose.

Odds are the pressure balancer is crusty/rusted too. Time to do some
maintenance.

Good luck,

Anthony Watson
www.mountainsoftware.com
www.watsondiy.com