Grohe Thermostatic Valve Problems

[Bruce Schroeder]

We have a new home with grohe thermostatic shower valves. The hot
water system is a Rinnai Continuum Instant instant continuous water
system (2 gas boilers in parallel) with a recirculating loop (very
long house).

Our Grohe thermostatic vavle is very unreliable. When first starting
a shower we get comfortable water temp. A few minutes into the shower
(probably the time it takes to run through the water in the recirc
loop) I get a blast of cool water (20 degree drop) that lasts for 20
seconds and then the water gets very hot and I have to reset the
thermostatic setting. It seems to me that we a presenting the valves
with temp changes in the hot water line (from warm in the recirc loop
to cool in the dead space piping between recirc loop and heaters and
then very hot from the heaters) BUT I expected the thermostatic vavles
to maintain the set temperature. We have replaced the cartridges and
even torn out the valve and replumbed it according to the Grohe rep
instructions. NO help. If I run the hot water in an adjacent sink the
shower turns around 10 degrees colder. These are very expensive valves
and I assumed they would work better than this.

Anyone have a similar experience or any advice? Does anyone have Grohe
thermo valves that are working properly with constant temp?

Do I need to rip out the valves and go with another vendor? Any
suggestions?

thanks
Bruce Schroeder
Greenville NC

[Mark Sauder]

We have 2 Grohe thermostatic tub/shower valves in our house.
They work quite well. We never get any temperature changes
while showering, but we have a normal electric hot water
heater. I can turn on the shower and after waiting a few
seconds (to purge the cold water out of the hot water line)
the temperature is stable.

You may want to double check that the hot and cold lines are
plumbed to the correct side of the valve. I replaced a single
handle Moen shower faucet and found that the hot was plumbed
to the right side instead of the left. It didn't matter
with the Moen valve because you can turn the cartridge around
to correct it. I don't know how the Grohe faucet would
react to being plumbed backwards, I discovered it while
I was installing the valve so I never ran it that way.

Good luck, they should work much better than they are
for you.

Mark