Hot Water Running Out

[valleycushion]

I can’t seem to get to the bottom of an ongoing issue in our house and was hoping for some help.

I have a 4 bed, built in 2013. We have a gas boiler and an indirect 250L water cylinder in an airing cupboard, controlled by Tado and gas central heating. Both recently serviced and seem fine. (Photos below)

We have always had the hot water on for 90 mins in the morning, kicking in 530am 30 mins before we shower and again in the evening at 5pm. Over the last 6 weeks or so I’ve noticed a lack of hot water during the day; so if I go to wash some stuff up at 3pm there’s often tepid or cold water. Equally the other morning I was up at 5am and the water was freezing cold. The night before the had barely been any hot water used (in fact the kids didn’t even shower that night) so I find it crazy that there was no hot water. Another example is today it came on for 90 mins this morning, we had two short showers , I've just gone to wash something up at 2pm and there's no hot water left.

The only thing running overnight is a new dishwasher, but surely that just uses cold water?

Some might say that we are possibly using more water than we realise, but we are in the same routine, if anything using slightly less since our kids now shower rather than bath.

To offset it I’ve been having the hot water come on for an hour during the afternoon, but this seems like a waste of money since it heats it at an expense but then seems like it does stay around.

To make matters more confusing, we appear to be using around double the gas for the same time last year. As an example in Sept 24 we used 159kw gas, Sept 25 it is 573kw. I think the months were comparable, we didn’t have the heating on so it’s crazy for it to be so much more.

Another example (these are comparable days with usage)
Oct 18 2024 shows
0600: 2.13kw
0700: 3.39kw
0800: 4.33kw

And for Oct 18 2025
0600: 7.69kw
0700: 17.93kw
0800: 5.57kw

So a pretty large difference. And again for the evening

2024:
1700: 6.26kw
1800: .32kw

2025
1700: 12.42kw
1800: 2.7

When the hot water is on, it is hot as expected. Not sure if this makes a difference but we have noticed the cold tap takes longer to give cold drinking water.

I can’t fathom what’s going on. My only assumption is maybe the water cylinder isn’t keeping the water hot, hence the big usage when the hot water kicks in. But the plumber said everything looked and seemed fine. Perhaps it's something to do with the two electrical switches on the wall?

Would love any advice, things to try, etc. I’d really not be having to pay for so much more gas, when we aren’t using anymore hot water than last year.

Thank you.

 

[Murdochcat]

This time of year the cold water entering your property is colder, meaning as the cold water enters your hot tank, it cools the water quicker.

Try extending the time the hot water is heated for during the night to see if it helps - and don’t forget once the water is up to temperature the boiler will switch off

 

[valleycushion]

This time of year the cold water entering your property is colder, meaning as the cold water enters your hot tank, it cools the water quicker.

Try extending the time the hot water is heated for during the night to see if it helps - and don’t forget once the water is up to temperature the boiler will switch off

Thanks, I've tried doing this, including running it for 3 hours in the morning, but have lost hot water by the afternoon and again running it for 4 hours from 6pm to 10pm, but freezing water at 5am. The boiler seems to be firing fine and heating the water as planned but it just doesn't stay hot and I feel like I'm paying lots of money to heat the water then it's just cooling back down.

 

[JohnD]

You have a well insulated, large cylinder. If it is going cold in less than a day, the hot water must be being used or leaking. Feel the pipes coming out of it. When you run a hot tap, the pipe feeding it will get hot. When you turn the tap off it will go cold. When you have not used any hot water for half an hour, and the boiler is not running, all the pipes should be at room temperature. Including the ones to the boiler and the radiators. Are they?

Do you by any chance have two bathrooms, or a bathroom a long way from the cylinder?

Feel the pump. Is it running?

 

[valleycushion]

You have a well insulated, large cylinder. If it is going cold in less than a day, the hot water must be being used or leaking. Feel the pipes coming out of it. When you run a hot tap, the pipe feeding it will get hot. When you turn the tap off it will go cold. When you have not used any hot water for half an hour, and the boiler is not running, all the pipes should be at room temperature. Including the ones to the boiler and the radiators. Are they?

Do you by any chance have two bathrooms, or a bathroom a long way from the cylinder?

Feel the pump. Is it running?

Thank you, yes it's going cold in a matter of hours, which isn't a good sign. There's no obvious leaks that I can spot, but there's a concern there might be something underneath us.

Everything is off at the moment, the cold water pipes feel very cold, the other pipes all feel room temp. I've just put the hot water on, and the bottom two pipes are warm (ones with the red arrows). After ten mins I still don't have hot water in my taps, will wait another 10 mins and let you know.

We have two bathrooms, both upstairs, on almost directly above the cylinder, one a little further away, but the second one is not used that often.

 

[valleycushion]

You have a well insulated, large cylinder. If it is going cold in less than a day, the hot water must be being used or leaking. Feel the pipes coming out of it. When you run a hot tap, the pipe feeding it will get hot. When you turn the tap off it will go cold. When you have not used any hot water for half an hour, and the boiler is not running, all the pipes should be at room temperature. Including the ones to the boiler and the radiators. Are they?

Do you by any chance have two bathrooms, or a bathroom a long way from the cylinder?

Feel the pump. Is it running?

Have had the hot water running for 30 mins now and it's warmer coming out the tap (not as hot as it normally is but getting there), the bottom two pipes are still hot and the pipe out the top feels hot when running the hot water tap.

 

[valleycushion]

You have a well insulated, large cylinder. If it is going cold in less than a day, the hot water must be being used or leaking. Feel the pipes coming out of it. When you run a hot tap, the pipe feeding it will get hot. When you turn the tap off it will go cold. When you have not used any hot water for half an hour, and the boiler is not running, all the pipes should be at room temperature. Including the ones to the boiler and the radiators. Are they?

Do you by any chance have two bathrooms, or a bathroom a long way from the cylinder?

Feel the pump. Is it running?

Another further update - the right hand side pipe is now hot

 

[Murdochcat]

Any changes of habits for using hot water?

I know my wife and son can use a huge amount of hot water having showers

 

[valleycushion]

Any changes of habits for using hot water?

I know my wife and son can use a huge amount of hot water having showers

Nope, if anything it's being used slightly less.

 

[Mister Banks]

Your gas usage for Sept 2024 looks extremely low. I live in a similar size house to you and my gas usage is around 500kWh in September. How are you measuring gas usage and how are you dividing the usage between heating and hot water?

 

[Johntheo5]

Nope, if anything it's being used slightly less.

I take it thats a unvented cylinder, if so, post the expansion vessel capacity, once this is known we can calculate the vol of (hot) water that should flow from any HW tap, shut the cold mains to the UVC, then open a hot tap and measure this vol of water, again open the cold mains for a few minutes, then shut it, ensure no one draws off any water, hot or cold, for 30 minutes or so then open a hot tap and measure this volume again, this will give some indication of any leaks etc.

 

[Murdochcat]

Nope, if anything it's being used slightly less.

So all your consumption is hot water heating only?

 

[flameport]

we have noticed the cold tap takes longer to give cold drinking water.

What exactly does this mean?
When the cold tap is turned on, cold water should come out immediately. If it's a mixer tap that's just been used for hot water, then perhaps a second or two to clear any hot water left in the tap body.
Anything longer that that and something is fundamentally wrong.

 

[Daveydub]

Is that a secondary return hidden behind the hoover?

 

[valleycushion]

Your gas usage for Sept 2024 looks extremely low. I live in a similar size house to you and my gas usage is around 500kWh in September. How are you measuring gas usage and how are you dividing the usage between heating and hot water?

Measuring the KWH using the Bright App and the British Gas App. Unable to divide between the two, other than the knowledge of when we have had the heating on (only in the last few days for a few hours a day) and when we haven't.