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A general query that I have been thinking about for a while.

I want my CH system (Vaillant ecoTec Plus open-vent boiler) to "come on" as follows as I find these timings work fine for me :

Early morning : heating 1 hour - hot water 1/2 hour

Evening : heating 1 hour - hot water 1/2 hour

What are the "pro's and con's" in terms of cost of gas and in terms of efficiency of heating and water temperature in having the heating and hot water "coming on" together as opposed to separately ?

Basically which is best ?

Many thanks.

If you have an S plan system heating water separately is more efficient

Neelix wrote: ↑Wed Oct 09, 2024 3:20 pm If you have an S plan system heating water separately is more efficient

I have a single 3 way valve - is that a Y plan ?

Yes

Taking account of the fact that I have Y plan system, can anyone oprovide a definitive answer to my original post ? Many thanks.

If you have the dhw come on first it will heat the water quickly, then when the heating comes on the full power of the boiler will heat the rads quicker.

gas4you wrote: ↑Fri Oct 11, 2024 3:13 pm If you have the dhw come on first it will heat the water quickly, then when the heating comes on the full power of the boiler will heat the rads quicker.

Many thanks for that but sorry to be dim (!) do you mean mean water on then water off then heating on. If so, that is fine in terms of "efficiency of heating water and rads", how about in terms of cost, presumably more gas is used with water and heating "on" separately rather than water and heating "on" together or is there another rationale ?

If you have the water on first for say 30 minutes, the water will go off on the cylinder thermostat.

If your house and water use are average then it is slightly more efficient to heat the water at the same time!

Because the boiler needs to run the pump for a shorter time and the boiler is less efficient when delivering a low output for just the cylinder.