I don't know anything about pre-heating, it's a condensing combi, turn the tap on and it heats the water.
Not sure if it is a WH100 or a WH130.
It's heating that runs up the units, not hot water.
I have no idea what the definition of a unit is, they are shown on the gas meter, and have almost doubled since we got our Ravenheat boiler from "A shade greener".
It's a 3-bedroom end-of-terrace.
I don't have a gas bill handy.
The problem with our "high efficiency boiler" that "A shade greener" claims to "save over £300 a year" is actually costing us hundreds of pounds MORE than our old, inefficient boiler. We have confirmed that no gas is leaking, we have no other gas appliances except a gas hob which is rarely...