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I have an ASHP for heating and hot water. Unless I use the “luxury” DHW setting, my shower mixer adds too much cold water as it requires the thermostatic valve temperature differential to be 12 deg C. Does any one know of a shower mixer that will work with a heat pump hot water cylinder feed, i.e with DHW between say 40 to 45 deg C, rather than at above 50 deg C?

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According to Google the ideal shower temperature is in the range 37 to 40C so you're looking for a differential  of perhaps 3-5C.  

 

This discussion from 2010 ended up talking about Thermostatic valves in general rather than just shower mixer but you get the idea..

 

https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5751

 

Quote

Justin: The Horne H25 seems to have 5C minimum differential (Their technical data). I guess this is a huge improvement on 12C, but is there anything which will operate down to even lower differential? 

 

Wookey: No, there was a long discussion about the minimum temp differential where Hannah from Horne tried to explain to us why it wasn't possible (due to the mechanical nature of TMVs) to build a TMV that closed the cold side entirely when the hot was barely hot enough. Personally I still didn't see whay it couldn't be done, but it definately isn't in anything you can actually buy. This is a huge disadvantage when you have a solar thermal system which often gets your water just about hot enough, but not 5-10C hotter then that. This is the main reason we have no TMV here. Perhaps electronic control is the only way to solve this (or more simply a manual bypass for borderline times).

 

Gavin:.. such things do exist, they're just called boiler TMV's, and not advertised for use within the actual hot water systems. definately not to be used as the only tmv on a solar system as they aren't fail safe, and could result in scalding water being fed through before the TMV kicked in properly. On a system where there is already a master TMV on the top of the tank, but someone wanted an additional tmv on a shower / bath or whatever, then this shouldn't be any more dangerous than, and realistically much safer than standard none tmv boiler/shower set ups.

advanced water systems sell them from watts industries for about £30 or so, and IIRC, they do 2 temp ranges - 49-79deg, and 39-something.

can't vouch for how they'd work as shower tmv's, but I've been using a couple for other purposes for a few months now and they seem to work fine, coped ok with being fed boiling water for a few minutes to test their robustness etc.

 

Maybe by now there are showers with electronic mixers that  can do it?

 

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44 minutes ago, KPy said:

DHW between say 40 to 45 deg C

Mine don't - I just heat to 50, then I can have the shower as hot as I want. Or use you luxury setting (whatever that may be). 40 to 45 degs in house is just too cold for DHW.

 

You set your DHW temp to suit your needs, not what someone else they set it to.

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If as you should you have a balanced cold feed to the shower you don't really need a thermostatic mixer, and ordinary one will probably do, that's all I have.

 

IIRC the cartridges for the common MIRA shower controls are interchageable in the housing so you might be able to convert it into a plain mixer by replacing the innards. Failing which I think at least the pipe centres are a common pitch so it might not be too difficult to replace the whole thing.

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We got caught out by this for our guest/family bath shower. The digital aqualiser one in our master works fine.

 

Still have guests complain they can't get it above 'warm'.

 

Think they are Paul Roche or Roche something or other ones. They weren't cheap either!!!

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1 hour ago, KPy said:

I have an ASHP for heating and hot water. Unless I use the “luxury” DHW setting, my shower mixer adds too much cold water as it requires the thermostatic valve temperature differential to be 12 deg C. Does any one know of a shower mixer that will work with a heat pump hot water cylinder feed, i.e with DHW between say 40 to 45 deg C, rather than at above 50 deg C?


I’ve seen this topic discussed here before and it did give me pause for concern. These thermostatic valves seem to need a minimum hot supply temp of 50°. Looking at the specs of some models and they want 60°. In the spec of one Mira model it states:

 

Quote

Minimum Recommended Differential between Hot Supply and Outlet Temperature: 12°C.


So a hot shower at 40° needs a minimum of 52° hot feed input. The Grobe Rapido T states in it’s spec that it only needs 2° different between the hot feed and the desired mixed output. 

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16 minutes ago, Alan Ambrose said:

I think this is still on topic: when buying these things, how do you ensure the  replacement cartridges are still around in 5-10 years' time?

But some at the same time.

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19 hours ago, Alan Ambrose said:

I think this is still on topic: when buying these things, how do you ensure the  replacement cartridges are still around in 5-10 years' time?

 

Buy brand name. The big manufacturers tend to use same cartridge in new designs for a long time.  Not so sure about unbranded makes.

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On 20/05/2024 at 15:41, KPy said:

I have an ASHP for heating and hot water. Unless I use the “luxury” DHW setting, my shower mixer adds too much cold water as it requires the thermostatic valve temperature differential to be 12 deg C. Does any one know of a shower mixer that will work with a heat pump hot water cylinder feed, i.e with DHW between say 40 to 45 deg C, rather than at above 50 deg C?

 

I had this exact problem with mine as well. I posted it on the heat pumps group and had 30 odd replies saying theirs was fine. The manual for mine stated hot water at 60 deg i think, with my old gas boiler producing 65 this was fine, but the 55 deg the hp produced it wasnt quite enough. 

 

I've since searched high and low for any that dont say high temps for the hot water and not found anything so gave up and blocked up the cool water inlet by around 50%. Works fine now.

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On 20/05/2024 at 15:41, KPy said:

I have an ASHP for heating and hot water. Unless I use the “luxury” DHW setting, my shower mixer adds too much cold water as it requires the thermostatic valve temperature differential to be 12 deg C. Does any one know of a shower mixer that will work with a heat pump hot water cylinder feed, i.e with DHW between say 40 to 45 deg C, rather than at above 50 deg C?

Have you tried setting the flow temperature via the adjuster that normally is accessed under the handle on quite a few mixers.  Allows you set the base mixing volumes. You would need to dig the manual for your specific mixer.

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  • 2 weeks later...

Hi.  Reading this topic with interest as I'm in the final stages of ASHP planning and wasn't aware of this potential issue.

 

I have Aqualisa thermostatic mixers (not digital) which quote a hot water supply temp of 55-65 DegC.  The ASHP will be an Ecodan 8.5kW with Ecodan 250 litre cylinder.

 

Am I to read from this that it's likely I will always need a top up to the DHW cylinder temp from the immersion element?  Or will the ASHP need to use additional electrical power to achieve required minimum temps?  Or worse change the showers?

 

Thanks in advance.

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Check the shower mixer instructions they should have a flow temp tuner (normally hidden inside) to ensure the centre of the temperature knob is at 34 or 36 degs. You can normally adjust this to it takes in less cold water and more hot.  I found storing in the cylinder at 48 the shower was just a little cool, while 50 was fine and could get it hotter than I required. It just a matter of a little fine tuning to get the sweet spot.

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Posted (edited)

Thanks for your reply.

 

Unfortunately no indication from instructions or sign of adjustment on the cartridge design I have.  Mine are a design that’s over 20 years older so perhaps before lower temp supply temperatures were even a consideration.


I’m going to run a few tests this weekend with the DHW cylinder set to lower temperatures and find out where the sweet spot is.

Edited by The Bin Man
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  • 2 weeks later...

The thermostatic Mira shower in one of our bathrooms (Screwfix stock code 43154) has a 12C minimum recommended difference between hot supply and outlet temperatures. It works fine (we have good mains pressure and have a balanced supply pressure on hot and cold). I've just bought another one for the bathroom I'm in the middle of refitting. Having said that, the 20 year-old ancient mixers originally installed in the house also seemed to be fine.

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