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Discuss Thermostatic Mixer Shower Removing non-return valves (gravity fed) in the Bathrooms, Showers and Wetrooms area at UKPlumbersForums.co.uk.

  1. Svenedin

    Svenedin Member

    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.
     
  2. Craig Watson

    Craig Watson Plumber GSR

    It's not the non return valves that were the issue, it's the wrong pump for the job. Do you have any other outlets attached to the pump or just the shower?
     
    • Agree Agree x 2
  3. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Neg head pump recommended due to these not needing flow to switch on
     
    • Agree Agree x 1
  4. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Still needs NRVs
     
    • Agree Agree x 1
  5. Svenedin

    Svenedin Member

    Just the shower is attached to the pump. It isn't the wrong pump. It's a positive head pump with a positive head and a flow rate in excess of that required to start the pump but with the shower NRV's in place there is not enough pressure to open them fully so there is insufficient flow to start the pump. It worked perfectly well before the shower mixer was replaced because the old mixer did not have NRV's and it works perfectly well again now that the NRV's are removed from the Grohe mixer.
     
  6. Svenedin

    Svenedin Member

    Why is that?
     
  7. Craig Watson

    Craig Watson Plumber GSR

    You dont adapt your shower to make the pump work, you pick the pump to suit the shower. A positive head situation doesn't always require a positive head pump, it's for this reason that negative head pumps are now classed as universal pumps so it avoids the confusion of when to use one.
     
  8. Svenedin

    Svenedin Member

    Ah but I already had the pump installed for several years prior to the change of shower mixer. It was Grohe's advice to remove the NRV's not my idea. Would you spend £400 for a new pump or buy a £5 12mm hex key and take the NRV's out?
     
  9. Svenedin

    Svenedin Member

     
  10. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Regs you don’t pick and choose them to suit
     
  11. Craig Watson

    Craig Watson Plumber GSR

    The previous setup was suited fine to the pump you had, upon changing the shower and realising it didn't work. A new pump should have been advised. I'm not saying that grohe are wrong, but I wouldn't have removed the nrv's.
     
  12. Svenedin

    Svenedin Member

    How do the regs apply when there is no direct connection to mains water and no connection to potable water?
     
  13. Svenedin

    Svenedin Member

    Well it is a workaround that has had a good outcome. Should the pump fail, as it will one day, maybe I'll replace it with a universal twin and if I really wanted I could put the NRV's back. That seems very unlikely though!
     
  14. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    I’m really not sure whether you’re just gloating or what?? The regs/NRVs also stop your cold water being heated and cooled repeatedly which can allow the growth of bacteria and nasties but you crack on. You clearly know best
     
    • Funny Funny x 1
  15. Svenedin

    Svenedin Member

    Absolutely not gloating and not saying I know best in the least. I don't see how the cold water is going to be heated.
     
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Users found this page by searching for:

  1. shower non return valves

    ,
  2. where is non return valve located in thermostatic mixer

    ,
  3. non return valve in thermostatic shower

    ,
  4. shower non return valve,
  5. do i need anon return valve for my mixer shower boilermate 11,
  6. non return valve on shower pump,
  7. installing a shower non return valve,
  8. what is a non return valve plumbing