Turn your preheat option off on your combi boiler!
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First off the pre-heat option is not used for instant hot water, they are used to provide high flow rates. The water from the pre-heat tank is added to the normal mains water hot water flow to get a greater flow rate so that these boilers can run more than one tap/shower at a time.
I measured mine with the pre heat on 24/7 and then off. The preheat tank 18 lites in my case used 30kwh per week so 1560Kwh per year or about 50 quid a year at current prices.
the pre-heat option is not used for instant hot water
Afraid you're wrong, pre heat in a combi boiler keeps up to approx. 3ltr of water hot in one of two ways.
One method is that gas is used intermittently to keep the the boiler and the water within, hot.
The second method is that the boiler has, within the casing, a miniature version of a hot water cylinder, complete with a small electrical heating element, when the hot tap is turned on water from the boiler passes through this ' small cylinder ' then on to the taps. When there is no call to the boiler for domestic hot water the heating element maintains the water temperature in the ' small cylinder' constantly at approx. 55d eg - 60 deg.
Both these systems are used simply to provide almost instant hot water at the taps, nothing more.
The preheat tank 18 lites in my case used............
I would be interested to know which boiler has an 18ltr pre heat tank.
The water from the pre-heat tank is added to the normal mains water hot water flow to get a greater flow rate so that these boilers can run more than one tap/shower at a time.
The thermal store system is designed around this principal, however, unless the thermal store has a reasonably substantial reserve, more than 18ltr, as soon as the reserve is used it will revert to the same flow as a conventional combi.
Are you getting mixed up between pre-heat and an external thermal store to supply the boiler such as produced by Alpha?
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I think some of the combi's have internal tanks even bigger than 18 litres. The Worcester Greenstar Hi Flo 550 combi has I understand a 50 litre internal tank!(this was discussed in a thread recently) which enables it to advertise a flow rate of 25 litres per minute - until that tank is empty at least!The technical specs say 41kW but this Highflow boiler although they call it a combi boiler it's not really a combi boiler. It's really a system boiler with a built in 50 litre cylinder of pre-heated hot water. It will run out of water eventually but it would take quite an effort. You could easily fill 2 baths with hot water and have the washing machine and dishwasher all going at once and it won't run out as it will catch up very quickly.0
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Well ive never heard of it as well, the WB junior certainly dosent have one.
What i try to do is make the boiler fire by increasing the temp for a few minuits before showering, then the water is almost instantly hot.0 -
I think some of the combi's have internal tanks even bigger than 18 litres. The Worcester Greenstar Hi Flo 550 combi has I understand a 50 litre internal tank!(this was discussed in a thread recently) which enables it to advertise a flow rate of 25 litres per minute - until that tank is empty at least!
Ahhhhh yes, storage combi boilers.
Been retired a good few years now.
Though I do try to keep up to date with everything new, I occasionally forget.
Now what did I come upstairs for. :shhh:
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It is a combi, its just not an instantaneous combi for the hot water supply
The reason for preheat is to prevent thermal shock which could damage the heat exchanger!!!!!!!!
Which is best save a few pence or buy a new boiler?
Armchair engineering can be dangerous!!!!!!!!!!!!!!Signature removed0 -
I was technically incorrect to say the water from the tank (called a heat bank in WB speak) was added to the mains waterflow, what I should have said is the heat stored in the heatbank is added to the mains cold water before it reaches the heat exchanger, because the flow of water through the heatbank is via pipes. So it is a pre-heat method but it is used to get the high flow, one aside may be instant hot water (but this depends on how long a heat exchanger takes to get to temp without a heatbank). Also the other reason that it is not used primarily for instant hot water is because as you said you only need a 3ltr tank for that. I was wrong when I said mine was 18ltrs it is in fact 60litres and according to the specs designed to provide the highflow rate of 18ltrs per minute for 10 mins.
I just read the technical specs for my WB highflow and what happens in practice is that with the heat bank up to the temp that the hot water temp gauge is set up. When hot water is demanded the mains cold flows through the heatbank (via coils) and then to the heat exchanger which is operating at max. Because the mains cold has been "pre heated" more water can flow through the heat exchanger than if it was at mains water temp, hence the highflow rates.
Yes you are correct that when the heatbank is at the temp of the mains cold water the divertor valve kicks in and the mains cold goes directly to the heat exchanger and the flow rate of hot water drops.0 -
It is a combi, its just not an instantaneous combi for the hot water supply
The reason for preheat is to prevent thermal shock which could damage the heat exchanger!!!!!!!!
Which is best save a few pence or buy a new boiler?
Armchair engineering can be dangerous!!!!!!!!!!!!!!
The reason for preheat is to prevent thermal shock which could damage the heat exchanger!!!!!!!!
Not correct Ted, the pre-heat, in a combi, is nothing at all to do with preventing thermal shock ! :rotfl:
Don't believe me, do some research, such as:
some combi boilers (Glow worm and Ideal Boilers) have a "pre-heat" facility that heats a small quantity of water ready for your use, this helps to eliminate running the tap for a number of minutes waiting for the hot water to come through.
If what you say is true, why don't the hundreds of thousands, or more, of boilers without the pre-heat function, constantly suffer from thermal shock induced failure?
They don't do they ?
This is taking into account the fact that in comparison, there are far fewer boilers produced with pre-heat.
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That is typical of someone who has to do research and has no experience
"SOME" is the keyword
Much as not all Combi's are instantanious and the older type have cast iron or steel heat exchangers and thermal shock can be an issue.
Try jumping into a freezing lake and see what happens to your body, dont bother to report back tho ?
I repeat to all posters as I have said on here ARMCHAIR ENGINEERING is dangerous, a diagnosis can only be carried out with FACTS of the issue by a QUALIFIED ENGINEER!Signature removed0
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