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Discuss Bath mixer shower head height changes temperature in the DIY Plumbing Forum area at PlumbersForums.net

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Situation: Had a boiler system conversion. From Potterton boiler with Gledhill storage tank with on demand hot water to Veissman Combo with on demand hot water. 2 bed semi with only myself and wife living here. Unfortunately used iheat service which has no real customer service. Have had the same plumber (good guy) back for service and asked him about this and he tried his hardest to work it out, but he suggested fairly expensive works that I wasn't sure would deal with this particular problem.

Heating works very well. Hot water good to a point, mostly just having to learn the limitations of a 29kw combi. Irritated by the long delay before hot water at taps, seems very wasteful of water. Mains flow measures at around 12lpm. Boiler copes with about 8lpm flow at taps to produce max temp rise. Not a big issue.

Problem: We use a hand held shower head fed through the bath mixer taps to wash our hair. So we get a comfortable temp through the taps by adjusting hot and cold flows with shower head at height of tap level, but then when we raise the shower head to above head level (about 18 inches) the temp increases to too hot.

I'm trying to understand the physics but finding it a little difficult. As I understand it there is a pressure drop at the shower head rose and the supply pressure of both hot and cold are the same. However there will also be pressure drops at each of the supply valves which will be dependent on their adjustment. So why does changing the height of the shower head change the differential flows of the hot and cold water? I suppose the pressure of each supply would have to be the same in order for the extra head of water to equally affect the two supplies. Oops, I think I've just understood it. But please let me know if I'm right.

Solutions:
1. I wonder if a thermostatic mixer tap would improve the situation but am not convinced because I'm not getting the physics.
2. Would putting flow restrictors or pressure limiters on each supply be an idea?
 

ShaunCorbs

Staff member
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Plumber
Gas Engineer
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Needs to be changed to a thermostatic bath mixer as it doesn’t take much to alter the heat

but 8lpm is a bit low of a flow rate should be around 12 summer time
 
Messages
4
Needs to be changed to a thermostatic bath mixer as it doesn’t take much to alter the heat

but 8lpm is a bit low of a flow rate should be around 12 summer time
Thanks for that ShaunCorbs.
I measured the flow rate at 8lpm when it was a bit colder than currently. So might be better now.
Do you know of any thermostatic bath mixers that are in the "Victorian" style? The ones I've found all appear to be ultra modern looking.
 
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Messages
1,760
Presume hot & cold both fed from mains, if not, with hot from the mains and cold from the cold water storage tank then the slightest change in shower head height will affect the cold water flow and the mixed temperature.
Don't know if the Viessmann has hot water temperature control, if so maybe set to 35C to 40C and run the hand held shower on hot water supply only.
 
Messages
4
Presume hot & cold both fed from mains, if not, with hot from the mains and cold from the cold water storage tank then the slightest change in shower head height will affect the cold water flow and the mixed temperature.
Don't know if the Viessmann has hot water temperature control, if so maybe set to 35C to 40C and run the hand held shower on hot water supply only.
Yeah. Both feeds are mains. Boiler does have Temp control. That's a brilliant idea. Thanks.
 
E

Eric Snowdon

bath/shower selector not isolating between taps and shower, suspect washer/ o`ring failure, but not sure how to dismantle Armitage Shanks sleave assembly.
 
E

Eric Snowdon

bath/shower selector not isolating between taps and shower, suspect washer/ o`ring failure, but not sure how to dismantle Armitage Shanks sleave assembly.
Did you come up with a fix for your problem?,
no
 

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