Hot water in tank but shower goes lukewarm after 10 minutes

ronancremin · 04-10-2017 10:28PM #1

I have a shower connected to a hot water tank via a pump. The shower has a Kludi thermostatic mixer, brand new. The filters in the mixer unit are brand new also.

The water starts out hot and stable but after about 10 minutes it quickly changes to barely lukewarm. At this time, if you test the water from the tap in the same bathroom it's still hot, so the hot water supply seems OK.

Water pressure is fine throughout.

Can anyone tell me what is going on?

One thing I've noticed is that the mixer control seems to be the wrong way around compared with the legend on the controller—counter-clockwise is the direction that makes my water hotter. The legend on the controller suggests that it should be the other way around. This is obviously not right, but does it explain the symptoms?

Picture of cylinder: IMG_1563.jpg

browner85 · 04-10-2017 10:33PM

Can you post a pict of your cylinder ?

ronancremin · 04-10-2017 10:50PM

browner85 wrote: »

Can you post a pict of your cylinder ?

Thanks for the quick reply! Can't get a pic right now (6 week old in my other arm) but will try later.

But I can tell you it's tall and thin with thick insulation on it. What are you looking to see?

ronancremin · 05-10-2017 09:47PM

Photo added.

05-10-2017 10:05PM

If you have a reasonably powerful pump you can drain the hot water cylinder in 10 minutes. How many bar is the pump? It should say on the pump

I know you said that there's hot water in the tap as the shower goes cold. It's possible that when you are coming to the last of the hot water that it would be hotter in the tap than the shower. The shower will have a temperature restriction. When the shower runs cold how much hot water is in the taps? If only a minute or so then you are just using the full tank of hot water

I don't see a flange on the cylinder either. The pump maybe sucking in air on the hot side

ronancremin · 05-10-2017 10:49PM

Thanks for your reply. The pump is behind panels but I'll find out.

I really don't think it's all getting used up though—what's left in the tank is enough for everything else for the whole day, and is plenty hot.

By comparison, the water in the shower goes cool very suddenly 5-10 minutes in. It feels too quick to be the end of the hot water supply. My suspicion is that the backwards hot/cold plumbing causes something in the thermostatic mixer to change after a while, but does that make sense?

browner85 · 06-10-2017 09:49PM

Sometimes the pump is fed from a side tapping about 3/4 the way up the cylinder to prevent it from pulling in air and there can be hot water left above this that could be teed off the expansion to feed the taps

Hot water in tank but shower goes lukewarm after 10 minutes

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