Grohmix not regulating temperature

[Kevro]

I've spent a few hours reading and searching, but haven't found a solution to the problem I'm having. Hopefully you guys and gals can point out where I'm going wrong.

I'm remodeling my second bathroom, and putting in another Grohe Grohmix valve, 34-436. I put one in my other bathroom a few years ago, and it's been working beautifully ever since, but I can't get this new one to regulate the temperature properly, and I'm at my wits' end.

What happens is, when I turn on the volume, no matter where the temp setting is, the water gets scalding hot (110+, my thermometer only goes to 110), then after 15-20 seconds, cools off to around 100 or so, and then is basically unresponsive to any temperature change inputs until I turn it off. I can leave it off for as little as 3 seconds, and upon turning it back on, it goes through the same process all over again.

I triple-checked that I didn't install the valve upside-down. I flushed everything out before putting the guts in it. I called Grohe and spoke to their excellent customer service, who sent me a new thermostatic cartridge, but that didn't fix the problem. I even tried the cartridge from my other bathroom, which is known to work perfectly, but the problem would still persist in the new valve body. I called Grohe back with this information, and they surmised that the problem must be outside the valve, and suggested there may be another fixture allowing hot water to get into the cold pipe or vice-versa, so I went around the house and turned everything else off, but that didn't do the trick either.

All the while, my other Grohmix still works wonderfully. Same house, same pipes, same boiler...

Do you guys have any suggestions of things I could try to pinpoint the problem? I'll try anything at this point! I'd be eternally grateful for any and all help you could provide.

[jadnashua]

Are you absolutely sure that the hot and cold going into the valve are on the correct sides? If you have shutoff valves, are they both fully open?

[Kevro]

Hi Jim, thanks for the response.

Yep, absolutely certain - I've re-checked it every day for the past week and a half (and again just now), hoping to find something wrong that I could fix. The hot water comes into the left side, marked "W" on top, in accordance with the installation instructions.

I even stuck my finger into the valve body on each side and felt a difference between left and right, and compared that to my other valve that works - both are installed the same way. The only difference is that the old valve is installed in a shower, utilizing the top outlet (with bottom one plugged), and this new one is in a tub/shower combo, using the bottom outlet (top plugged), with the twin-el going to a diverter tub spout and shower riser.

The service shutoffs are fully open - slots horizontal, parallel with the flow of water.

Should a thermostatic valve allow scalding hot water through it at all?

Could an internal machining flaw cause the erratic behavior, letting hot water get past the thermostatic cartridge somewhere? Hmmmm....I should inspect for damaged or missing O-rings.

Here's something that's weird - if I have the water running, and I close the cold shutoff, the water that comes out is warm, not hot. When I do that without the cartridge in there, the water is scalding hot - how is the cartridge cooling that water down with no access to cold water? It doesn't make sense!

Another straw that I'm grasping at: the mixing valve on the boiler is kinda siezed up, so I can't adjust it, and there is no check valve on the cold input leg, which should be there, per the instructions. Could a pressure differential between hot and cold be causing hot water to flow backwards through the cold pipe and into the cold side of the shower valve, so the cartridge only has hot water to work with? And if so, why doesn't my other Grohmix exhibit the same problem? Would shower head vs. tub spout pressure differences have an impact?

[jadnashua]

Try turning any single handle faucets in the house to one side (i.e., either all hot or all cold), or shut off their supply valves. Include the washing machine(s). What brand are these faucets? Some are known for cross-over, and could be the reason you've got hot coming in on the cold side. Depending on pipe run and locations, you might not notice it at the other bathroom.

As I understand it, this type of valve senses the outlet temperature and moves a piston based on the setpoint and the outlet temperature (Grohe cartridges are, I think made with a wax in them that melts and allows the piston to move - they have a spring to pull it back). If it is getting hot on the cold inlet, it cannot mix. It might even get hotter, since it would be adding more cold (which, if hot, would just make it hotter).

On some valves, they say never use one side or the other...do the instructions allow use of the one you have selected? It is fairly common to not allow both, but sometimes it requires a specific one, regardless.

[Kevro]

Thanks, Jim, for some more ideas. The other faucets in the house are a Kohler in the kitchen, and Delta in the other two bathrooms and laundry sink. They are all single-handle.

I have tried turning everything in the house off - all the faucets, including the washer, laundry sink, and even the dishwasher and ice maker (since they branch off of the kitchen faucet shutoffs), as well as the service stops on the other shower valve. I left the toilets and hose bibs on, since they're only connected to cold water anyway. This had the effect of slightly improving the situation for a minute or two, and I almost started celebrating, but then it went back to its old ways of ignoring temperature changes.

What do you mean, "one side or the other" - the inlets or the outlets? This Grohmix has volume and temperature controls integrated into one rough-in valve, so the only inlets are for hot and cold, but there are two outlets - top and bottom. The instructions say that only one can be used, and the other must be plugged, but it doesn't say that one of them should never be used.

If it is getting hot on the cold inlet, it cannot mix. It might even get hotter, since it would be adding more cold (which, if hot, would just make it hotter).

- That does sound like what's happening. I would love to put in temperature and pressure gauges on each side of the shower valve to observe exactly what's happening when everything's under pressure...

So by turning off all the other fixtures, I think I have eliminated them as being the cause (unless Kohler and Delta allow cross-over?), and the only other place that hot and cold water could mix is in the tempering valve (with missing check valve). I think I'm going to see if I can close off the cold input of the tempering valve somehow, to eliminate any possible cross-over. There is no valve in place to do so, so I might have to get creative...

[Kevro]

I called in a plumber, and he noticed that the valve works perfectly when water is going through the showerhead (which is limited to 2.5 GPM), and the problem only occurs at the tub spout. When you open the volume control to approximately 2.5 GPM, everything works fine at the tub spout as well.

The plumber replaced the broken tempering valve on the boiler, which was apparently only really designed as an anti-sweat device for a toilet, but the previous installer used it for the entire house's hot water. We now have a real mixing valve in place, with domestic hot water reliably regulated at 125 degrees. He also noticed that the aquastat on the boiler is inaccurate, allowing it to get up to 220 degrees, even though it's set at 190 (which is also too hot).

Fixing the temperature settings on the boiler, along with the new mixing valve, have cured the problem. Thanks for your help in narrowing down the problem - this is a great site!

[bmeehan1]

I have an existing Grohmix valve installed in my main bathroom shower/tub. After developing a dripping, I replaced the two (hot and cold) stops as well as the paraffin cartridge. Now the valve will not regulate temperature. When I have both service valves full open, the water never gets above, say 100 degrees. I tried to compensate by throttling back on the cold service valve, but then the water gets very hot and is still not temperature controllable. In reviewing these forums, I have decided that the service valves need to be full open. I am also thinking that the volume of water I am getting out, my have something to do with my problem. Just by looking at the water flow, I think I am getting more volume out of the spout than I got before I replaced the parts.

Another thought I had was that the handle I have only turns about a half turn. It seems like the cartridge will allow for a turn and a half of adjustment. However, even with the handle off and making adjustments with a wrench, I cant make it work. Any ideas?

[hj]

Normally you use the wrench to adjust to a 100 degree temperature, then install the handle with the index at 100. Once that is done the numbers should be accurate.

[bmeehan1]

Is it possible to be flowing too much water to control the temperature?

[jadnashua]

Unless you water pressure is like a pressure washer, no. There are internal restrictions in the valve...as I said (I think, elsewhere), I think you may not have the cartridge seated properly or have it reversed (possible on some, but not all). It's also possible that when you had it apart and turned the water back on, you dislodged some gunk, and have it now lodged in the valve somewhere.

[bmeehan1]

It wasn't me that you told that to and I dont recall seeing it, but I do appreciate the help. Ill try to pull it apart and see what I can find. Thanks

[steverobb]

I have a Grohmix 34 474. When set temp to anywhere from 80-120 degrees the water is 104 degrees. When set to 70, the water comes out 98. The sink in the same bath is 123 degrees. What is the fix?

[Tom J.]

Here is the adjustment that worked for me. I think the same can be used to calibrate the thermostat control. I am a homeowner, not a plumber.

Background: After replacing stop valves to fix a leaking faucet, the same thing happened to me. Even though I did not touch the Thermoelement Cartridge, after re-assembling the control unit, the faucet only delivered steaming hot water, no cold. I confirmed cold water was flowing through the pipe and the stop valve, but was simply not reaching the Thermoelement Cartridge to be mixed with hot water. I tried a number of things but finally learned the "trick" from a helpful Grohe customer service rep. You simply need to turn the nipple at the outermost end of the Thermoelement Cartridge (clockwise for more cold) to adjust the intake setting.

The brass nipple, nozzle, or cone -- it looks sort of like an empty bullet casing with a hole in it -- is located at the outermost end of the Thermoelement Cartridge. It extends from the center of the 15/16" hex nut that you _would have to_ place your socket wrench over IF you wanted to remove the Thermoelement Cartridge itself. (You do NOT need to remove the Thermoelement Cartridge to adjust the nozzle!) The nozzle has 2 flat edges for a wrench. Take a monkey wrench and turn the nozzle slightly until you get the desired water temperature.

Few tips:
1. You need to turn off the water to remove the control/handle mechanism. You can do this easily by removing the 2 screws from the oval escucheon (the fancy dress plate against the wall), then turning the escucheon 90 degrees will reveal access to the water shut off valves -- turn these shut off valve "screws" 90 degrees to turn off the water. It is a nice trick.

2. The hand lever to the control unit has an accompanying clip that must be snapped into its proper place to hold the lever in. Doing this may be a bit tricky, because the yoke mechanism is spring loaded and is pushing itself forward and may conceal the "groove" the clip must be fitted into.

3. Note that to make the adjustment above, you need access to the brass nipple on the end of the Thermoelement cartridge. You do not need to dis-assemble the entire unit.

Hope this helps.
Good luck.