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)

 

[townfanjon]

Mike , what make is the tank ?

 

[Mike Hart]

I've searched around the blue cover but cant find a make, I've unzipped the blue cover and there is a metallic Flexiseven cover wrapping the brass tank - I'll cut it open if you recon the make will be under the Flexiseven cover? (The flat was build in the early 90's).

 

[drip-dry]

is it on the mains or tank fed ?

 

[Mike Hart]

It's fed from the mains.

There's no branding on the tank cover, flexiseven on the material under the cover, no way of looking at the copper tank without cutting the flexiseven material off.

 

[jtsplumbing]

Don't think fault is with tank, more than likely you have a blending valve on system [TMV] that needs adjusting or is faulty

 

[Mike Hart]

an image of my hot water tank:

add h t t p ://s14.postimg.org/zdw8he3y9/IMG_20150216_WA0001.jpg

 

[Mike Hart]

There is a device on the hot water outlet, it has a green dial on top, Hot water passes threw it horizontally but it is also has a cold water feed from the bottom. Could this be my TMV? Should I adjust it? This doesn't explain why I only get about 10min hot water, if something was wrong with this shouldn't I just be getting tepid water all the time?

 

[Deleted member 64964]

Have you got a mixer shower in the house? It's probably blending try isolating the shower if so or turn it from hot to cold vice versa.

 

[townfanjon]

we are guessing a bit at the moment but if its a thermal stores, as jts says it will have a blending or mixing valve on it somewhere.

if you cant find one , report back and possibly with a pic

 

[Mike Hart]

I cant upload images, not allowed.

The shower has 2 dials, one is off/on the other is hot/cold. Its its usually set to be as hot as possible.

The hot water outlet on the water tank has a T shaped junction with a green dial on top. Hot water passes through it horizontally off to the rest of the house. There is a cold water feed from the bottom. Could this be a CMV? Could this be at fault? Sorry if i'm repeating myself.

Thanks for all the help so far.

M

 

[townfanjon]

Mike , just back to basics for a moment , i know you have cold water at the taps but is the cylinder hot ?? .
un zip the insulation, at the top of the cylinder there is probably a lid which will cover a header tank , just make sure it is approx half full of water, the ball valve is probably knact so if it is , fill it with a jug .
Then try holding the hot pipe leaving the blending valve, and see if it keeps hot.

 

[jtsplumbing]

Is this a new build flat ? if so contact the builder ! ask other tenant's if they have same system & how it works, at the moment we are just guessing, a picture speaks a thousand words

 

[Mike Hart]

The tank is warm to the touch. The sample of water I've just drained from the bottom is warm.

Insulation unzipped, lid off the header tank. Its got 6cm of water - I've tried to top it up to 15cm (half-way) but the water is staying at the same level because of a side outlet its draining out of. It has its own feed that had been turned off... so I turned it back on and the tank started self filling. Maybe the previous owners had been let down by the ball valve and cut of the feed manually.

Its taken about 20min but the level is now half way. Needles to say I've run the hot tap and its cold - but I expected it to be - what with the big top up.

I'll give an update tomorrow...

 

[townfanjon]

Jts, somehow mike emailed me the pic , trouble is , I don't know how to put it on here lol

 

[Mike Hart]

Morning update: We put the plug in the bath to collect the shower water this morning and got half a tub of water (just above the jet nozzles) before it turned tepid.

 

[townfanjon]

Mike, the cylinder should be just about too hot to touch, just warm sounds like it's a simple immersion heater thermostat is needed.
Get one fitted and then see what happens , at this stage don't have anybody touch the blender , they are pretty reliable .

its possible it's the programmer but a sparky or heating engineer can check it

 

[Mike Hart]

I've changed the thermostat in the overnight heater and its set to max 70. I've tested the voltage to the heater also and both the overnight and the boost are ok.

The mixer - the previous owners had it set to all the way anti-clockwise and this is how I've left it as turning it clockwise just introduces even more cold water.

If there was a way to cut off the cold water supply to the mixer I guess that would help determine the true temperature coming from the tank.

So tomorow morning the tank should be almost too hot to touch? I'll report back.

 

[Mike Hart]

I can confirm the tank was very hot to the touch this morning. Disappointing temperature shower however.

The make of my mixer is 'oventrop' and judging by how cold the feed to it gets when the hot's running I'm sure its letting through too much cold.

 

[townfanjon]

Mike , now the cylinders hot it's time to adjust the blender, beg borrow or steal something to measure the temp of the water leaving the cylinder . ( I use something like the temp probe you would stick in some food to check it's cooked )
Get the hot tap running and adjust the temp to about 55 degrees ish.

When you say the shower temp was poor, if you have hot water at the taps, it's possibly the shower that's faulty or wants setting up similar to how you set the blender up. not at 55 DEGREES though lol

 

[Mike Hart]

Sorry, I have been misleading when I say the shower runs cold, in reality all hot taps in the flat run cold but this is only after the showers been running for 15min or so.

Thats why I'm finding this so confusing, if I have a full tank of hot water, and have a mixer (set to max) that sends out a relatively hot water mix - so why after 15min do I get the drop in temperature and why cant I stop the mixer taking on too much cold water.

Even if I do get a temperature gauge on the hot water this wouldn't solve the issue of the duration of temperature.

 

[drip-dry]

If blending and balancing valves Ok....Think maybe you will find the non return valve on the hot supply side to the shower mixer is sticking open,allowing the cold mains water to flow through to the hot pipework side and over powering the hot supply at outlets.....

 

[townfanjon]

As drip dry suggests , you may be getting hot / cold crossover . This can be tricky to diagnose , but it still could be the cylinder blender. Depending on your level of plumbing skills ( LOL ) this may need a plumber, but to diagnose the cylinder valve rather than something going wrong with mixer taps and showers , I would temporary did connect the HW pipe leaving the cylinder , put a stop tap or similar on it and run a pipe to drain , run it and just see what happens , if you run out of HW in 15 mins and the cylinder is still hot, the blender is knact, if you don't , the problem is somewhere in the house . Good luck

 

[Neil K]

From the sounds of it he's got a thermal store. In which case the hot will be the same pressure as the cold ie. They'll both be mains pressure. The water in the store doesn't go anywhere and it needs to be heated to the highest possible temperature to instantaneously heat the cold water mains in the coil to Hw. The green oventropp valve is a blending valve.

 

[Mike Hart]

 

[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