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daftdog

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Scottish power now have available on their customer web site a daily consumption graph.
I have turned off our central heating part off our combi boiler. However looking at recent graphs I can tell when I shower and my wife washers her hair these usually at approximately same times every day. What is noticeable also is the "Dry Cycling" of the boiler after about "20:00"untill about "08:00" each morning. Is it possible to switch this Dry Cycling off. I have searched on line but cant find an answer.
As user of power for heating etc you must be faced with a similar fuel usage. One on line site indicates that dry cycling can increase fuel consumption and costs by as much as 15%.
How much is this adding to your fuel costs. Is this something that you as specialist in boiler controls could advise us all that a simple and practical solution to turn off the Dry cycling and reduce the currant fuel costs of the average household.
 

MARK.B.

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If there is no requirement for hot water between those hours could you simply just switch of the boiler until needed the next morning, bit of pain to do as you have to remember to do it before jumping in the shower, but it would cut any costs involved with dry cycling , not a boiler expert but i can't see that it would cause any problem in doing that.
 

daftdog

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I intend to add a an adjustable on/off timer into the power feed cable To turn the boiler foo every night at 2100 and on each morning at 0700 until winter arrives. More details to follow
 

Spectric

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"Dry Cycling" of the boiler
Please explain further because a combi boiler should only consume gas when there is a demand for heating, in the case of the combi this is when water is flowing and is controlled by the divertor valve assembly. With the central heating part this should be controlled by a room stat and not the boilers water temperature setpoint.

In a conventional system using a system boiler and hotwater cylinder the control system must be such that the boiler only runs when there is a demand, this being controlled by using appropriate zone valves and room / HW cylinder thermostats. These systems tend to use less gas than the combi.

When boilers used heavy cast iron heat exchangers there were systems that just allowed the boiler to maintain a constant water temperature whether there was any demand from the system or not which was inefficient and you could experience kettling in the boiler . With the modern lightweight heat exchangers this is definately not advisable and you must have a good bypass in place to prevent kettling.
 

Pedronicus

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Please explain further because a combi boiler should only consume gas when there is a demand for heating, in the case of the combi this is when water is flowing and is controlled by the divertor valve assembly. With the central heating part this should be controlled by a room stat and not the boilers water temperature setpoint.
'Dry Cycling' on a combi boiler is not related to the heating circuit but to the hot water circuit. It is designed to heat a small amount of hot water stored in the boiler to provide a quicker draw-off at the outlets. When turned off it will mean there is a longer wait at the outlets for hot water to be delivered and a waste of water. However, water is cheaper than gas so I advised all my customers to turn DC off.
 

Spectric

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That to me sounds totally contradictary of the combi boilers so called efficiency, it is just a waste of gas and is like leaving your engine runing just in case you want to use the car. I do not like combi boilers and will always advise having a system boiler and sealed system(unvented cylinder) installed and on large runs then just use hot water recirculation. Other advantages are off the shelf components such as pumps and valves, you are not tied into having to buy the boiler OEM's parts and you have a nice big tank of water ready that has been heated slowly and not with a huge woosh of gas consumption.
 

Pedronicus

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That to me sounds totally contradictary of the combi boilers so called efficiency, it is just a waste of gas and is like leaving your engine runing just in case you want to use the car. I do not like combi boilers and will always advise having a system boiler and sealed system(unvented cylinder) installed and on large runs then just use hot water recirculation. Other advantages are off the shelf components such as pumps and valves, you are not tied into having to buy the boiler OEM's parts and you have a nice big tank of water ready that has been heated slowly and not with a huge woosh of gas consumption.
Roy, couldn't agree with you more, dear chap. However the main (selling) advantages of a combi are instant hot water when required; no space to be allocated for a hot water cylinder (and the associated heat loss from said tank); a dry roof space with no tanks/pipework therein. They are ideal for 1 bed flats but not for 4 bed houses. I also would never entertain one in my own house but, during my 40+ years in the heating industry, they have become very popular. The biggest problem with them is that the majority are thrown in by firms who do not appreciate the finer points of water hydraulics relating to pressure and flow rates hence hubby, having a shower upstairs, is suddenly doused in cold water as wifey turns on the hot tap in the kitchen downstairs.

Anyway back to the OP's question. If he advises of boiler make & model one may be able to advise on the turning off of the 'dry cycling' or 'keep warm' function that is costing him money.
 

John Brown

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That to me sounds totally contradictary of the combi boilers so called efficiency, it is just a waste of gas and is like leaving your engine runing just in case you want to use the car. I do not like combi boilers and will always advise having a system boiler and sealed system(unvented cylinder) installed and on large runs then just use hot water recirculation. Other advantages are off the shelf components such as pumps and valves, you are not tied into having to buy the boiler OEM's parts and you have a nice big tank of water ready that has been heated slowly and not with a huge woosh of gas consumption.
Genuine question: why would heating water more quickly use more gas?
 

Pedronicus

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Ideal Isar HE24 Purchased 07/08/2017
Not familiar with this boiler but, after reading the User Guide & Installation Manual it would appear that the DHW Preheat cannot be turned off as is possible on other makes/models of boiler. Short of turning the boiler on/off switch to the 'Off' position the Preheat runs for a couple of minutes every so often 24 hours a day to keep the plate heat exchanger hot.
 

Spectric

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Genuine question: why would heating water more quickly use more gas?
The way it was explained to me is that it is like getting to the top of a hill, you either go direct or take the longer leisurely path, one is a lot harder but quicker.

Another way is to think that you have cold water and you want to instantly deliver hot water, this requires a lot of energy compared to gently raising the temperature using a cylinder, a small system boiler may be 18Kw but an average combi boiler is 25+ Kw. The other point to make is that the combi also will have a shorter lifespan but they are a good earner for many heating engineers as it's easily done in a day.
 

John Brown

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The way it was explained to me is that it is like getting to the top of a hill, you either go direct or take the longer leisurely path, one is a lot harder but quicker.

Another way is to think that you have cold water and you want to instantly deliver hot water, this requires a lot of energy compared to gently raising the temperature using a cylinder, a small system boiler may be 18Kw but an average combi boiler is 25+ Kw. The other point to make is that the combi also will have a shorter lifespan but they are a good earner for many heating engineers as it's easily done in a day.
Well I'm not convinced. In terms of foot pounds, or whatever the metric equivalent is, the long way and the shorter way up the hill are equal. Also, there is some formula to do with raising the temperature of a certain amount of water by one degree, which also is not, to my knowledge, time dependent.
 

Spectric

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the long way and the shorter way up the hill are equal
Not true, the shortest route is a straight line but it will be the steepest whilst the longer route may zig zag to reduce the incline making it easier.

Also the combi has to raise the temperature of moving water from about 10° C to setpoint whilst a cylinder is full of static water at a much higher starting temperature.
 

John Brown

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Not true, the shortest route is a straight line but it will be the steepest whilst the longer route may zig zag to reduce the incline making it easier.

Also the combi has to raise the temperature of moving water from about 10° C to setpoint whilst a cylinder is full of static water at a much higher starting temperature.
Ok. I give up.
 

Jacob

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Roy, couldn't agree with you more, dear chap. However the main (selling) advantages of a combi are instant hot water when required; no space to be allocated for a hot water cylinder (and the associated heat loss from said tank); a dry roof space with no tanks/pipework therein. They are ideal for 1 bed flats but not for 4 bed houses. I also would never entertain one in my own house but, during my 40+ years in the heating industry, they have become very popular. The biggest problem with them is that the majority are thrown in by firms who do not appreciate the finer points of water hydraulics relating to pressure and flow rates hence hubby, having a shower upstairs, is suddenly doused in cold water as wifey turns on the hot tap in the kitchen downstairs.

Anyway back to the OP's question. If he advises of boiler make & model one may be able to advise on the turning off of the 'dry cycling' or 'keep warm' function that is costing him money.
No prob with 4 beds. We have a combi in our chapel conversion and it heats the top 2 floors 2000 sq ft and does the hot water.
Yes the shower temp suddenly shifts but you just have to tell everybody not to touch the taps whilst you are in there!
 

Spectric

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They waste it on social media and living in make believe worlds because the real world is to hard to face.

It is not that long ago that people had outside toilets and no running water, running hotwater came many decades later and initially only for the very wealthy so has all this so called progress actually backfired and made us all soft.
 

Sandyn

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It is not that long ago that people had outside toilets and no running water, running hotwater came many decades later and initially only for the very wealthy so has all this so called progress actually backfired and made us all soft.
I remember using outside toilets when I was young. A small wooden shed with a hole in the seat, newspapers and a pail . In winter, it was freezing, as the cold wind whistled between your legs. In summer, the smell and flies!!! I'm very happy to be soft.
 

Oldman

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Its a sidestep to using pre heat for hot water on combi boilers but has anyone here installed a combisave?
This fits into the hot water out 15mm from the boiler (within 750mm) and once setup throttles the boiler water output down when a tap is opened until the water temperature reaches 42 deg C then allows full flow. This saves dumping up to 8ltr of cold water down the drain while waiting for the boiler to catch up with the sudden demand and to a degree saves gas as well.
Yes, without fitting one of these you can just turn the hot tap on a little to restrict flow and hopefully the boiler has fired but if the water flow wasn't enough to trigger the burner you will waste even more water having to crack it further. The rest of the family wont bother anyway, they will just turn the tap on full and wait.
 
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