Combi-boiler hot water - pls settle argument!

A_fiend_for_life

Lozenger wrote: »

Is it hugely expensive to leave the water on all day?

We have a fairly new combi (Highflow 440) and my other half is used to the old tank system and goes crazy at me if I dont immediately switch the hot water off as soon as I have had a bath... I thought the whole point of it was instant hot water but he insists on it being off til we need it (then I forget to switch off).

It's causing arguments - please help!!:D

Personally I prefer to switch the combi off if it is not required. It's effortless and saves money.

It might be worth investigating the savings obtainable from a shower (or a mixer ?) though avoid a power shower as they can be as inefficent or worse than a bath.

Some people find mixers a faff but they are cheaper.

Shared baths are fun but could be expensive in the long run.

A bucket of water calms a crazy person down.:cool:

redpete

aelitaman wrote: »

I answered the question that the OP asked "Is it hugely expensive to leave the hot water on all day with a combi."

I thinlk you actually answered the question "Is it hugely expensive to leave the hot water on all day with a combi that's got an integrated hot water reservoir and a long pipe run to the tap and you run the hot water tap to fill the kettle."

The length of the pipe run is irrelevant assuming that the boiler is on when you draw water from the hot water system, you would 'waste' as much hot water whether the boiler is left on all the time or not.

redpete

A_fiend_for_life wrote: »

It might be worth investigating the savings obtainable from a shower (or a mixer ?) though avoid a power shower as they can be as inefficent or worse than a bath.

One of the advantages of a combi is that hot water is delivered at mains pressure. Isn't it unusual (ill-advised even) to fit a power shower (if you mean a pumped shower system) with a combi?

Dave_save

I thought these combis had a pre heater system which heats the small reservoir to ensure you get almost instant hot water. With this turned off there is quite a lag before the boiler heats the water sufficiently. Mine has a timed programme to allow this pre heat to be off at periods you are unlikely to draw water. eg you wouldn't want the pre heater ON if you are away or out at work. I would think the saving is smallish per day, but over a year it could add up to a few ££

Cardew

Possetjohn wrote: »

Hi all,

Followed this discussion with interest!

Cardew while I agree with your comments about the gas consumptions with in aelitaman's post surely the heat losses in the small storage tank in some combi boilers is not the only thing you have to consider. Every time the water in this tank drops below the preset temperature the boiler has to fire again to reheat it, and therefore reheat the water in the primary and direct hot water heat exchangers.
Although the natural convection in these forced air primary heat exchangers is low there will be some and because of the inherent efficiency of the condensing heat exchangers. I think this is the part which will give the higher gas consumption/heat losses.

My first year's experience of these combi boilers shows the production of hot water is quite quick even after a cold start in the summer so I would not bother with it.

Possetjohn,

Yes I certainly agree with you that there will be losses from the reservoir and in the boiler firing up.

I was simply questioning the figure of 4.7kWh per day.

Anyway I looked up the data on the Highflow 440.

It has a 12 litre reservoir which will be heated at the temperature set by the hot water temperature control switch.

However it has an 'ECO' button which switches off this facility - the downside is that it will take much longer to get Hot water to the taps/shower and of course a lot of(metered?) water is wasted.

It doesn't give any figures for the loss from the reservoir/boiler firing. However for much of the year the heat loss from that reservoir is not 'lost' as it heats the fabric of the house. It is in effect a small 'radiator'.

Lozenger

Ha, I knew I was right. Thankyou to all who took the time to answer - especially the lengthy calculations. I dont know much about the facts and figures, but I do know it takes longer to run the water to get it hot when its just been switched on.

Victory is mine :rotfl:

aelitaman

Cardew wrote: »

Possetjohn,

Yes I certainly agree with you that there will be losses from the reservoir and in the boiler firing up.

I was simply questioning the figure of 4.7kWh per day.

Anyway I looked up the data on the Highflow 440.

It has a 12 litre reservoir which will be heated at the temperature set by the hot water temperature control switch.

However it has an 'ECO' button which switches off this facility - the downside is that it will take much longer to get Hot water to the taps/shower and of course a lot of(metered?) water is wasted.

It doesn't give any figures for the loss from the reservoir/boiler firing. However for much of the year the heat loss from that reservoir is not 'lost' as it heats the fabric of the house. It is in effect a small 'radiator'.

The expansion vessel is 12 litres. The heatstore is 51 litres.