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Discuss Remove TMV under bath in the DIY Plumbing Forum area at PlumbersForums.net

Messages
2
Hi All

I'm about to fit a thermostatic bath/shower mixer tap to create a shower over the bath. As it's a new build property there is already a TMV under the bath to limit the temperature of the hot water.
Should I remove the TMV under the bath and rearrange the pipe work to give single hot and cold feeds to the thermostatic tap or can I leave the TMV in place. Any advice would be greatly appreciated.
 
Messages
906
1. If you leave the TMV in place, the hot will always be limited to the temperature set on the TMV. It can never be delivered any hotter.
2. If you are adding the shower, but leaving the bath in place, you could take the hot and cold feeds from the input side of the TMV, which effectively cuts it out of the shower circuit. The bath would remain limted by the TMV, thus reducing the risk of scalding.
 
Messages
2
1. If you leave the TMV in place, the hot will always be limited to the temperature set on the TMV. It can never be delivered any hotter.
2. If you are adding the shower, but leaving the bath in place, you could take the hot and cold feeds from the input side of the TMV, which effectively cuts it out of the shower circuit. The bath would remain limted by the TMV, thus reducing the risk of scalding.
Thanks for the reply.

The shower is a combined thermostatic bath tap and shower. The Aqualisa Midas 110 (pic). Which I assume would regulate both the shower and bath filler, doing away with the need for the under bath TMV altogether. However, it would be easier if I could just leave it in place. The TMV is a Pegler which is preset to 43⁰C according to the spec. From reading through various sources I believe this is a max preset temp of most thermostatic valves. Though I understand that there is the possibility to adjust. Assuming I'm happy with the temp range, will this arrangement have any effect on the flow rate or cause me any other issues. Thanks in advance.Screenshot_20210518-161420_Chrome.jpg
 
Messages
906
Check that the shower mixer will work with hot at 43 degrees. From memory, they sometimes require a greater hot / cold differential or a minimum hot water input temperature.
 

Ben-gee

Esteemed
Plumber
Messages
1,992
Also check, some of those mixer are thermostatic on the shower only. The bath filler is often not, this allows bath to be topped up with hotter water and also will fill a bit quicker.
 

Ric2013

Plumber
Messages
3,133
Some thermostatic mixers will always deliver no hotter than 10 degrees below the inlet hot water temperature. Others, 2 degrees.

You might accept a maximum bath tap water temperature of 41 degrees, and it will be fine for a shower. If it's effectively limited to 33 degrees, it will be terrible.
 

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