Pressurised system dumping hot water?

[Loofah]

I have a pressurised system, tank in utility room and boiler in loft, and generally everything works fine.
Every now and then, about once a week maybe, all the hot water disappears. I can be using it and then 15 mins later there's no trace of even warm water being available. Today for example, everyone had their shower (only 2 adults) and ran a bit for some washing up then by 1130 absolutely zero hot water. Do these systems ever dump their contents? On other days there's no issue at all and we certainly haven't emptied the tank which is a Stelflow twin std, 250l. boiler is a worcester bosch
I'm at a loss, knowing next to nothing of the system

 

[JohnD]

what hours are on the timer?

 

[ETAF]

about once a week maybe, all the hot water disappears

Is this always the same day of week, maybe look at the timer as suggested
is it a week timer or 24hours
we have a timer for the week, so we can set different On/Off times for each day of the week for Hotwater & CH
However, what times do you have shower etc - we can run off our little hotwater tank on a couple of showers , washing up etc.

 

[endecotp]

Do these systems ever dump their contents?

No.

2 people x 10 minutes each x 12.5 litres per minute = 250 litres.

Try measuring how much water your shower uses, with a measuring jug and a timer.

 

[fixitflav]

I have a pressurised system, tank in utility room and boiler in loft, and generally everything works fine.
Every now and then, about once a week maybe, all the hot water disappears. I can be using it and then 15 mins later there's no trace of even warm water being available. Today for example, everyone had their shower (only 2 adults) and ran a bit for some washing up then by 1130 absolutely zero hot water. Do these systems ever dump their contents? On other days there's no issue at all and we certainly haven't emptied the tank which is a Stelflow twin std, 250l. boiler is a worcester bosch
I'm at a loss, knowing next to nothing of the system

I would try running the hot water 24/7. If the cylinder is well insulated I doubt if you'd notice any increased gas usage.

 

[Loofah]

Thanks. I'll double check the timer but think it's set the same across the week and I haven't noticed if this is on one specific day so I'll check that. I'm just finding it weird that with the broadly same routine (and much shorter showers than 10 mins!) that occasionally the hot water disappears. It's not even mid-use, like running a tap and it runs out, it's being used then next time the hot water is freezing and just not available.

I assumed the storage tank has it's own insulation but it doesn't have any extra lagging.

 

[fixitflav]

I can't think of an explanation, but just one thing - has it always behaved like this or is a new problem?

I assumed the storage tank has its own insulation but it doesn't have any extra lagging.

Unless it's very old, it will be pre-insulated with some sort of foam. That's a big cylinder, more typically about 1/2 that volume. According to the website, it can also use solar heating (in addition to gas boiler). It probably doesn't explain your problem, but do you have that?

 

[Loofah]

No, just supplied via the boiler. If the system doesn't dump it then it must just be a mucked up timer as there's no way we use that much water. I have yet to check! It's the suddeness of no supply that I'm baffled by

 

[Loofah]

Overdue update on this - it turns out my builders decided to connect a blue shutoff valve to one water supply pipe and close off the other. They just fitted it to the hot and not the cold so the washing machine has been supplied by hot water which might account for the loss in hot water! Discovered by chance when getting a new machine. I had previously also changed timer settings which seemed to alleviate the issues a bit but no issues at all since swapping water supply connections

 

[Mottie]

My mate connected up his washing machine the wrong way round (when you had hot and cold feeds to washing machine) and wondered why his clothes were coming out hot. Did yours? Also, if you have your hot water cylinder temperature set too low, you will run out of hot pretty quickly. Try turning the temperature up and/or leaving the hot water permanently on.