Boiler (oil)

HillStreetBlues

Not combi.
Currently heating on 8am off at 10pm. Water heated into tank an hour a day 9am to 10am.
Does it matter how it's set up with heating on first, water on first or both start at same time?

QrizB

I don't know the first thing about your boiler but I have heard from others on this forum that oil boilers don't generally modulate, so they're either on or off. If this is the case I'd definitely run the HW cycle within the general heating period, not before or after it.

If you start them both simultaneously then you'll have the HW tank load on the system at the same time that the boiler is working hardest to heat your house. In principle this could extend how long it takes for your house from getting warm. So running it as you currently do, with the HW cutting in an hour later than the heating, will help avoid this.

Depending on where your HW tank is and how lossy it is, you might consider extending the heating time. If waste heat that leaks from the tank is going to be useful (if unintended) space heating, it doesn't really matter how long the HW cycle runs for.