Combi Boiler

[vulcans]

I have a gas combi boiler, and I know that when I have my central heating on, that it is going to use a certain amount of gas. What I would like to know is, if I have my water heating on at the same time, will it use the same amount of gas, or will it use more. Logic tells me that it should be using the same amount, but since I started using them at the same time like this, my gas bill seems to have got higher. I wonder if it would be cheaper to revert back and use an immersion heater for the hot water, using it at off peak times, ie Economy 7.. Any advice would be helpful, thanks in advance.

[buildersmate]

Think of it like this, some gas produces heat that is used to go into the CH system; some gas gets used to heat the DHW. So logic shouldn't tell you it will use the same amount of gas, since you are requiring more heat from the system.

In general with a modern gas condensing boiler, DHW heated via the boiler will be cheaper to generate than that from Economy 7 - off-peak electricity is still one of the most expensive fules, per unit of heat generated.

[Dodger666]

With a combi boiler, I thought that when you opened a hot water tap the central heating stopped. It certainly does with my Ferroli.

If I open a hot tap the boiler stops if the central heating is on. Then relights without the pump running to supply the hot water. After closing the hot tap the boiler "rests" for about 30 seconds then the heating starts again.

Perhaps some boilers are different.