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Hot water issue, never seen this before: Grant Heat Pump and Cylinder

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(@marvinator80)
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This is so weird. Cylinder is heating up fine. Temp says 53 right now. But when I run the cold tap it’s hot only for a short period and then cools down very quickly so I have lukewarm water at best. 

Anyone ever had this?

Baffled of Ayrshire


   
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Mars
 Mars
(@editor)
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Any updates on your situation?

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(@marvinator80)
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Posted by: @editor

Any updates on your situation?

not yet. It did resolve itself for a while yesterday but is back to the same issue now. 

We have had water pressure issues in the area due to power outages affecting pumping stations but I just don’t know. Our plumber was too far away yesterday to come but hopefully will come today.

 


   
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(@hughf)
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do you have a blending valve (TMV) on your hot water supply from the cylinder?

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(@iancalderbank)
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Are you sure you've describe it the right way round? Your description says the cold tap runs hot then lukewarm? Did you mean the hot tap? If so then either there's not enough hot water in the cylinder or something is blending in cold when it shouldn't be, such as a TMV.

If it IS the way you described it please confirm.

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(@marvinator80)
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@hughf I would expect so. It’s a Grant pre-plumbed cylinder and I do suspect the issue is with blending. 

I’m waiting for plumber to take a look now.


   
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(@marvinator80)
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@iancalderbank yes, that’s right Ian. I mistyped in my opening post. It is the hot tap. Runs, gets hot and then quickly becomes lukewarm when I know for a fact there is plenty of hot water in the tank. 


   
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(@iancalderbank)
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Posted by: @marvinator80

@iancalderbank yes, that’s right Ian. I mistyped in my opening post. It is the hot tap. Runs, gets hot and then quickly becomes lukewarm when I know for a fact there is plenty of hot water in the tank. 

ok no worries . in which case I concur with yourself and hughf, blending valve is the first place I'd check. you should be able to feel the temperature of its 3 ports change over time as you run the water.

 

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(@marvinator80)
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Thanks everyone. I’m not sure what the blending valve looks like on the grant set up. I guess a plumber will know. 😬😬😬

IMG 4587
IMG 4586
IMG 4585

   
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(@iancalderbank)
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@marvinator80 its not a grant specific component. Find the hot water output pipe coming out the cylinder and follow it.

something like this

image

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(@marvinator80)
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@iancalderbank I can’t see anything like that. This is the bit where the water seems to mix, but I’m not sure. I guess if that’s faulty it will need replaced. Trying to gently hurry up my plumber.

 

IMG 4588

   
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(@iancalderbank)
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@marvinator80 no thats one of these 

stops your cylinder blowing up if its gets too hot or high pressure due to some control error.

one of the pipes will go via a short route to outside. "emergency dump pipe"

My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs


   
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