Combi Boiler gas consumption confusion
in LPG, heating oil, solid & other fuels
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Our Combiboiler apart from providing central heating is also set up to provide hot water by the 300L indirect unvented cylinder.
At present boiler powers on twice a day to provide hot water and again twice a day to provide central heating-but at different times.
Hence our gas bill is higher.
I was wondering if I could get boiler timings synchronised to provide central heating AND hot water for the cylinder at the same time.
We have Worcester 38D classic combi.
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Regarding your query, heating the hot water and trying to heat the house at the same wont save you any money, it will just take longer to heat the house and the tank but you'll probably use the same amount of energy.
Given that your central heating and hot water are controlled independently it is very likely that each has its own on/off valve so both could be open at the same time. Some systems for heating and hot water use a single valve with two positions (i.e. 3 ports) but I think that would require a single controller that does both central heating and hot water.
Therefore I think it is highly likely that you could run both heating and hot water at the same time but your gas bill depends on the amount of heat drawn by your cylinder and by your radiators and I don't think running them simultaneously or at different times will make any difference. [Edit: I have assumed your central heating has some sort of thermostatic control, either a room thermostat or radiator thermostats or both. If not then those are what you need to save on gas]
Your combi boiler will never know if it is heating the central heating or the radiators or both so some comments about boiler flow and temperature are based on a misunderstanding and wrong.
I'm guessing it takes four hours or so to fully heat your 200l hot water tank from cold, as most tanks only have a 3kw coil unless it's fitted with a larger high efficiency heating coil.
Doing the sums you'll still need 24kw to heat everything to the same temperature as it was before, so sharing the output from the boiler to the heating and hot water wont save you any energy but it could take twice as long to heat them (or only get them half as hot in the same time)
The way to save energy, is to reduce your hot water temperature, dont use so much hot water (take fewer showers and dont stand in them for so long), turn your heating down and improve your insulation.
In fact any combi boiler can be configured as a "system" boiler by treating the cylinder as a second zone on the central heating.