Strange shower temp change

[Cain2k]

I have a Grotherm 3000 valve (34909) in a shower that was installed many years ago. A little while ago, it started only putting out hot water. After a little research, it seemed like the cartridge was the most likely candidate.

When I opened it up and tried to turn off the supply locally using the check valves, hot water kept flowing. So I shut-off the main and removed the check valves. They were both in bad shape (mineral deposits, damaged screens). I decided to replace both check valves (1411600M) and the cartridge (47450), which was easy enough.

Strangely, I am still unable to stop the water by closing the check valves. And now, I am only able to get cold water. I removed everything turned on the water to flush any mineral deposits, and put it back together. No change.

Any thoughts on why the change from only hot to only cold, why the check valves aren’t working, or how to resolve?

Thanks in advance.

 

[WorthFlorida]

Valve body shutoffs are call "stops" not check valves. Here is a parts diagram for your 34909 but it does no show stops, only filters or screens. Grotherm has valve bodies that do have stops. It's possible that stops were added outside the valve body. This is a thermostatic cartridge required by law and it's an anti scalding device & feature. A sudden drop in pressure on one side closes off the other side to prevent an extreme temp change and shock. Usually, as you have replaced, is the cartridge gets gummed up. Without pictures, etc its hard to say. It could be the stop valve is bad, plugged up with mineral deposits. If there is a stop valve a seat washer could have disintegrated plugging things up or the cartridge went bad.

A slight possibility the cartridge in installed 180 degree off. Was the replacement cartridge a Grotherm brand?

https://www.faucetshark.com/Grohe-34909-Replacement-Parts-s/6558.htm

 

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[Cain2k]

Thanks for the reply. I’ll try to take pictures today once I can shut-off the main again w/o protest from the family.

I probably got confused about the stops from looking at another Grohe valve diagram before I found the one you are referencing. I assumed they had the same function, but understand that not the case.

The replacement cartridge is the Grohe part from the diagram you referenced: 47450000.

I suppose it is possible that cold was nearly totally block before and is now flowing fully while hot still has some blockage.

Valve body shutoffs are call "stops" not check valves. Here is a parts diagram for your 34909 but it does no show stops, only filters or screens. Grotherm has valve bodies that do have stops. It's possible that stops were added outside the valve body. This is a thermostatic cartridge required by law and it's an anti scalding device & feature. A sudden drop in pressure on one side closes off the other side to prevent an extreme temp change and shock. Usually, as you have replaced, is the cartridge gets gummed up. Without pictures, etc its hard to say. It could be the stop valve is bad, plugged up with mineral deposits. If there is a stop valve a seat washer could have disintegrated plugging things up or the cartridge went bad.

A slight possibility the cartridge in installed 180 degree off. Was the replacement cartridge a Grotherm brand?

https://www.faucetshark.com/Grohe-34909-Replacement-Parts-s/6558.htm

 

[Cain2k]

I tightened the filters (now that I know they aren’t stops), adjusted the temperature per the Grohe manual, and it’s working.

Thanks for help.

Thanks for the reply. I’ll try to take pictures today once I can shut-off the main again w/o protest from the family.

I probably got confused about the stops from looking at another Grohe valve diagram before I found the one you are referencing. I assumed they had the same function, but understand that not the case.

The replacement cartridge is the Grohe part from the diagram you referenced: 47450000.

I suppose it is possible that cold was nearly totally block before and is now flowing fully while hot still has some blockage.

 

[WorthFlorida]

I took a closer look at the parts diagram and it does read #5 as check valve, my bad. Glad you solved the problem.