Worcester Greenstar Oil boiler - Hot Water query

13 Oct 2020
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United Kingdom
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Hi There,

I have a Worcester Bosch Greenstar Heatslave 25/32 oil boiler. Never had an oil boiler before and last heating system we had a hot water cylinder.

just after some advice on the heating of hot water. We can programme the hot water to set times, but it always seems to run cold unless we have it it set to ‘on’ constant. We have a nest 3rd generation installed with heat link in to the boiler, but this only seems to be able to control the heating. We recently had an engineer around to fix a small leak on the boiler, he stated that if we didn’t want the hot water to run out, have it set to always on. Question is, is this burning oil unnecessarily, or is it simply only heating when there is a demand for hot water? That is what I’m struggling to understand. If there was a hot water cylinder, there is water stored to heat, why is there even an option to heat hot water on this boiler when it’s a combi? Any help much appreciated
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There is a pre heated storage tank that must be heated before hot water is available. Water is pumped from this and through a plate heat exchanger. Once depleted there is a reheat time delay. It is normally advised to set water to come on half an hour before heating.
A gas fired combi is low water content and heats up as needed.
Thanks for response. Still slightly confused. When you say have hot water set to come on half an hour before heating, do you mean for instance if showering at 6.30am, have water set to come on at 6am and heat for half an hour, Then if running a bath at 7, have water heating set to come on at 6.30pm for half an hour? In your opinion is having the hot water set to always on wasting energy/ making the boiler work needlessly? Thanks
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This depends on your lifestyle. If you want to shower at 6:30, then set your water for 6:00. Leave it on until 8:00am and you can run your bath and have some capacity for incidentals. If you then set it for 1/2 hour before you are due home and let it run for 3 hours or so, then you'll have water for washing up, etc. Most of my customers with oil combi's switch the water on at about 6:00 am and leave it on until 8:30 or 9:00pm. If you are not running water all day, then you'll very little heat from the heatstore, but will have the convenience of hot water at the turn of a tap.

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