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Discuss Thermostatic Mixer Shower Removing non-return valves (gravity fed) in the DIY Bathroom Remodelling Advice area at PlumbersForums.net

I am not a professional plumber but I thought I would share this tip as it defeated the professional plumber who installed my new shower and there seems to be no information about this on the internet.

I should say first (before I get flamed) that non-return valves (NRVs) are mandatory where a mixer valve is supplied by mains cold water and they seem to be built-in as standard to modern shower valves. The valves are there, as I understand, to prevent the possibility of the mains cold water becoming contaminated (from say a shower head falling down a nearby toilet) or where there is unequal pressure in the hot and cold feeds which could lead to crossflow (usually cold into the hot).

Anyway, that is not the situation in my house. I have an old style gravity fed cold feed from a tank in the loft and an indirect vented hot water cylinder in the airing cupboard. To boost the pressure I have a twin impeller, positive head pump (Stuart Turner Monsoon) which means the hot and cold pressures are equal (pump has dedicated supply).

I had my bathroom professionally refurbished and a new Grohe Euphoria thermostatic shower installed. The old shower had worked very well but that was not the case with the Grohe unit. When the shower valve was opened the pump would not start unless the shower handset was unhooked and held below the mixer valve. A nuisance. I telephoned Grohe and they told me that this is because the NRVs will not open fully and provide sufficient flow for the pump to start because they need more head of pressure to open than I have under gravity. Grohe told me to remove the NRVs from the mixer valve. They seemed very familiar with the issue.

There are 3 NRVs in my mixer valve. One at the outlet and removed by disconnecting the handset hose (very easy). The other 2 in the inlets (for me very difficult). To remove the inlet NRVs the bar mixer has be taken down from the wall connections and then the inlets removed from the mixer bar. The inlets are threaded with left hand threads (clockwise to remove) and require a 12mm hex key. They are extremely tight (a long hex key is better, Matador make a good one) and there is only a shallow "socket" for the hex key because the NRVs prevent the tool from getting a better seat. Maybe I am a weakling but it took all of my strength to get the inlets off! After I did the first I decided it would be easier to destroy the NRV in situ with a screwdriver and needle nose pliers so that the hex key could seat more easily. Then any debris can be removed once the inlet is off. The O-rings should be greased with silicone grease prior to reassembly.

Now that I have removed the NRVs the shower works perfectly. Pump starts instantly. I wish I had known prior to installation as it would have saved grief. I also wish there had been something in the instructions about this. Not everyone has mains pressure hot and cold. There are a lot of old houses around still.

Hope this is of some use to someone in the same situation.
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer

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