Hot water in the tank, but not at the taps...

[Mike Hart]

We have a huge electric water heater in our new 2 bed flat yet after a couple of 5-10 min showers the water runs tepid.

The tank is on a timer to heat up at night (immersion heater thermostat set to about 70).

To get to the bottom of this today I began to drain the tank (in order to inspect the lower heating element) and before long I had removed a bathtubs worth of nice hot water... So I stopped draining the tank, switched the water back on and ran the shower - It was hot for 1min and then ran tepid. I then went back to the tank drain tap to see what temperature came out and it was nice and hot.

Im sure I have a full tank of hot water in there, so why am I not getting it at the tap?

After leaving all taps alone for an hour, I ran the hot tap and got nice hot water for about a min and then it ran tepid again.

Its almost like the cold water feed is interfering with the hot some how.

Anyone got any ideas how I troubleshoot this?

Thanks

Mike (confused recent home buyer)

 

[Mike Hart]

 

[Mike Hart]

 

[Neil K]

Yes that's a thermal store. The top part is just the make up tank that fills up the store, the larger bottom part. The water in the store, bottom part doesn't go anywhere it stays where it is. There's a coil in the store, cold water mains goes in and comes out piping hot because it's heated up instantaneously by the surrounding water in the store (which doesn't go anywhere ) . For this to work successfully the water in store should really be heated to 80-90 degrees C not 60-70 degrees C. The green blending valve simply mixes cold water with the Hw coming out of the thermal store so the resident doesn't get scalded. If you've got a mixer shower or taps to do this anyway then the green blending valve should be left to its highest setting. Have you got a gas boiler in the property?

 

[Mike Hart]

Right, I am learning. So no we don't have gas, the flat is electric only. Do I need to swap out the thermostats for ones that'll let it reach 80-90? Seems incredibly inefficient. All our taps and our shower are the blending type.

 

[Neil K]

If all your taps and showers are the blending type then there's no need to blend it when it comes out of the thermal store ( otherwise you're blending it twice ) So on the top of the blending valve you've got a plus and a minus, you want it turned all the way to the + mark (hottest ). So the only thing heating the water in your thermal store is those 2 immersions. I hope they are on a timer. Basically the thermal store needs to be heated up and at its hottest at your peak demands ie. Immersions set to come on an hour before you use your Hw, two - three times a day. I don't know if you can get immersion heaters with cutoff temps 80-90 degrees C, maybe other forum members might know. Yes it's inefficient because electricity is always the most expensive method of heating water. Shame you don't have a boiler or alternative heat source, then the immersions would only be a top up or emergency back up.

 

[townfanjon]

Neil, with the greatest of respect pal, a lot of that above in my opinion is wrong .
you must have a blender on the cylinder .
you shouldn't just turn it up to the hottest ( temp must be checked)
thermal stores, cylinders are best kept hot all the time, it doesn't actually need a timer unless the customer is on an off peak tariff,
all thermal stores stats will have cut outs and the cylinder temp needs to be about 70 min / 80 degrees

 

[Neil K]

You must have a blender on the cylinder yes but as OP points out all his Hw is blended at all his outlets and he's running out of it too quickly. If you want to instantaneously heat mains water then your primary heat source needs to be higher than 70 degrees C

 

[Mike Hart]

Thanks for all your help guys...

This system is on a Eco 7 tariff, as we are showering in the mornings (after the timer has switched off) there is nothing keeping the storage water hot. SO I imagine this is half the problem.

The other half of the issue is the mixer doesn't help, putting my hands on the pipes - as the hot tap is running - its frustrating to feel the mixer adding freezing cold water to the already dwindling temperature of the hot.

Finally we have the issue of the thermostats being limited to 70.

 

[townfanjon]

You must have a blender on the cylinder yes but as OP points out all his Hw is blended at all his outlets and he's running out of it too quickly. If you want to instantaneously heat mains water then your primary heat source needs to be higher than 70 degrees C

I doubt if they are blended, sound more like mixers to me lol

 

[townfanjon]

Mike, get a new blender that now sounds like the problem

not sure what you mean about the stats, thermal stores work at a much higher temp then your conventional cylinder.

 

[Mike Hart]

The thermostats in my store have the adjuster on them, from 30 to 70, how's it supposed to run hotter than they allow?

 

[townfanjon]

If those are the original stats from the manufacturer , 70 will be ok . Those rod type stats are nt the most accurate things anyway , 70 could mean 80 or 60 lol