What's normal for Grohe Thermo valve?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by prescottrecorder, May 24, 2006.

  1. prescottrecorder

    prescottrecorder New Member

    Messages:
    11
    I have a new shower installation using a Grohe 34 902 mixing valve. It's a 3/4 " variant to supply two shower heads and lets you dial in the desired temperature.

    What I've noticed is wild fluctuation of temperature after flushing the toilet. It's briefly colder than normal, then too hot, then back and forth with some variations in flow thrown in before stabalizing after about 30 seconds.

    Does anyone have any experience to say whether this is normal or what could improve the situation if it's not? If it is normal, I'm pretty disappointed in Grohe.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    I've used several of those, both overseas and here in the US...I've not noticed that. I'd call Grohe and talk to one of their techs. It is possible that there is some dirt in the pressure balance portion of the valve, preventing it from performing its function. One hotel I was in in London had this type of valve, and although the volume changed as people were flushing, etc., the temp was pretty stable.
  3. prescottrecorder

    prescottrecorder New Member

    Messages:
    11
    Thanks. It didn't seem normal to me. I've sent an email to Grohe. I didn't see a phone number for tech support. I'll look at the site again, though.

    anyone gone through the process of cleaning dirt out of it?
  4. prescottrecorder

    prescottrecorder New Member

    Messages:
    11
    Grohe tech support tells me that the valve has no pressure balancing capability and that it's normal for the temperature to fluctuate when the toilet is flushed. It supposedly has only an anti-scald function that kicks in only if the cold water supply stops due to a pipe break.

    Can anyone verify this?
  5. prescottrecorder

    prescottrecorder New Member

    Messages:
    11
    Although phone tech support from Grohe says it's normal, email tech support says it's debris in the valve and sent instructions for cleaning. I think I'll try the cleaning approach.
  6. prescottrecorder

    prescottrecorder New Member

    Messages:
    11
    Well, for the benefit of anyone who in a future search finds this thread and wonders how it ended:

    I took the valve apart and cleaned the check valves and temperature cartridge with running water. There was a little debris in there.

    It now works better when the toilet is flushed. Before, I got a long series of temperature oscillations. Now there is a brief period of hotter temp when the toilet is first flushed followed by a brief burst of cold and short overshoot to hot before stabalizing after the toilet stops filling. Each temperature fluctuation lasts about two seconds.

    In my other shower, which has a pressure balancing valve, I don't feel any difference when the toilet is flushed, so the Grohe falls short in that respect, but at least now it's not going crazy during flushing.
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