Same problem - I called Grohe
I am having this exact same problem. The 34436 was installed in May of 1997. When the lever is turned all the way to the left the tub spout leaks. My assesment was the same, I concluded it was the stop valves. I tried to find the right sized o-rings, but to no avail.
I ended up calling Grohe parts (630) 582-7711 and asked for technical assistance. They agreed that it was the stop valves (part no. 08.355) and I asked if I could replace just plunger in the stop valves. They said no, but there is a washer set that I can use to replace all of those washers and o-rings. THe part number for that is 47.045, and it lists for $26.00. It has the o-rings for the hot and cold sides and the replacement screens for the stop valves.
I am curretly looking for local distributors so I can buy one on the way home from work.
Per the Grohe technician's advice I plan to replace the rings on the plunger and lube them. I may replace all of the o-rings that are available in the set. I have seen no evidence of pitting or corrosion in the valves, so I am thinking it is just the rings.
So far Grohe's assistance has been very helpful for me.
I do find it kind of strange that a several people have written here with pretty much the same problem in the past couple of months.
I will write back with my results.
Groche 34436 (weak water flow)
I bump into this thread while researching how to trouble shoot a recently developed weak water flow from a grohe 34436 valve. I have eleminated any blockage in the hand shower head and flex host. One noticable symptom is that adjusting temperature may result in a temporary increase in water flow.
User "lambtron"'s 10-05-2006 posting referenced a stop valve filter. Where is such filter located?
Currently, I have disassemble sufficient parts to expose the frontal wax cartridge, and shut off the hot/cold service stops.
What is a safe way to take out the wax cartridge?
Below are the URLs to the valve schematics and part list:
Thanks in advance.
Groche 34436 (weak water flow) - resolved
After some tinkering, I was able to access the stop valve, and find that the
filter is a piece of wire mesh wrapped around the middle of the valve stem.
The filter is cloaked with debris. After cleaning the filter and flushing the
valve, the water flow is backed to normal.
The comments in this forum has been extremely helpful.
I also have a problem with my Grohe model 34-436
It started as a leaky faucet and the valve being to tight for my wife to turn on the faucet. So I ended up changing the thermoelement cartridge and the stop valve and my faucet had no leak and was easy to turn on the faucet lever. But now my hot and cold doesn't work I only get one temperature in water. I just can't figure out, could it be the service stop or should I give up? Any ideas I would appreciate any advice that could be given? Thanks.
Tips for removing thermostatic valve?
I replaced the o-rings in the stop valves last night to fix the leaking shower, but this morning all I got was hot water out of the tap. My guess is that debris got into the thermo unit, but I am unsure how this item is removed. I tried loosening it with the 22mm hex, but it only budged a degree or two - is this a threaded unit? This is an older model (my guess is 10-15years old put in by the house's prior owner).
Is there any trick to remove the cartridge?