Water Not staying hot for long with Tempest Cylinder 250L

chris1012

I have had a tempest Unvented Cylinder installed in our cellar just over a year ago when we had our loft converted.
From what I remember, The cylinder provides hot feed to only our two of our three bathrooms and kitchen sink.

The Cylinder is scheduled to heat up for an hour every morning at 5am-6am, hot water draw off from combi boiler.
During the summer, we would manage to have 2 showers in the morning lasting 10-15min in total for both showers, run one bath that takes 5-10mins to fill and a 5-10min shower for our kids in the evening.

Now it is Autumn/Winter, I am finding that come the evening the water from the cylinder is luke warm and therefore not hot enough for a shower or bath.
Is this normal?

Our Cellar is not insulated and would naturally is the coldest room of the house.

Should this be expected or could there be something wrong?

Robin9

One hour is not enough to heat the whole tank - try 3 or 4

chris1012

We were told 1hour is fine and it states the same in the user manual.
Would have helped if I stated the hot water is drawn off from the combi boiler as well.

shaun_from_Africa

Robin9 wrote: »

One hour is not enough to heat the whole tank - try 3 or 4

My tank (150 litres) takes slightly over an hour to go from cold to 45c.

There are a few things that will determine exactly how long it takes:

Size and efficiency of heater element,
volume of water,
initial temperature of water, (which in the winter could vary greatly from the summer months),
heat loss from the tank.

Chris, is your tank insulated?

chris1012

shaun_from_Africa wrote: »

My tank (150 litres) takes slightly over an hour to go from cold to 45c.

There are a few things that will determine exactly how long it takes:

Size and efficiency of heater element,
volume of water,
initial temperature of water, (which in the winter could vary greatly from the summer months),
heat loss from the tank.

Chris, is your tank insulated?

Hi Shaun,

The tank is insulated from within and I belive 85% of the hot water is drawn off from the combi boiler

southcoastrgi

The hot water from the combi won't run out it will run slower but it will still work, think to yourself what happens if you add cold water to hot water what happens ? You are adding cold water to the hot water in your cylinder, welcome to winter

thorganby

I believe that you are confused how your hot water system actually works.

Think of your 250 L tempest unvented cylinder as a water heater, not a hot water storage cylinder that stores water for you to use.

Mains pressure cold water flows though a heat exchanger in the cylinder which needs to be kept very hot to heat up the cold water as it passes though.

I doubt that you have a combi boiler, what make model is it?

Your comment that "85% of the hot water is drawn off from the combi boiler" makes no sense with type of cylinder.

The gas boiler temperature needs to be set to at least 75C to ensure that there is a tank full of hot water in the heat store, so that it can heat water from cold.

Post some pictures of your set up.

keith969

thorganby wrote: »

Mains pressure cold water flows though a heat exchanger in the cylinder which needs to be kept very hot to heat up the cold water as it passes though.

Well that's not how mine works, or any other pressurised unvented system I've seen. Hot water from the boiler goes through a heat exchanger (a coil) in the cylinder to heat the water in it.

neilmcl

I'm a bit confused as to your setup (possibly you are too), particularly with comments such as "85% of the hot water is drawn off from the combi boiler". I might be wrong but if you're saying you have a combi as well as this cylinder could it be that this is a direct cylinder just feeding the upstairs bathrooms and the combi boiler is completely separate for heating and hot water for the kitchen etc?

If this is the case, it doesn't sound unreasonable that the immersion turned on for an hour early in the morning isn't enough to supply hot water in the evening especially after it's been used to feed 2 showers and a bath in the morning, this time of year. This would especially be the case given that it's kept in an uninsulated loft.

neilmcl

keith969 wrote: »

Well that's not how mine works, or any other pressurised unvented system I've seen. Hot water from the boiler goes through a heat exchanger (a coil) in the cylinder to heat the water in it.

Unless its a direct cylinder.

chris1012

Apologies for my novice description and info.

So I have had a look at the manual and it is a Telford Tempest 250l indirect cylinder.
We have a combi boiler (Potterton Titanium) but has been modded to work as a system boiler and we have one of our three downstairs toilers using hot water directly from the combi boiler so the 'diverter valve' is used regularly.

According to the manual it states 'Time to re-hear from cylinder from 75% draw off boiler is 25mins or time to re-heat from cold 35mins'.
This is what I understood as the water being drawn off the combi boiler.

The combi is used for scheduled downstairs underdloor heating, feeding one bathroom with hot water and all the rads in the house.

The Cylinder provides hot water to 2 bathrooms and the kitchen sink.