Replace rotary timer and install thermostat

[D_Hailsham]

AVC, clearly a typo. Unless there is also a manufacturer called ACV.

There is a company called ACV which was founded in Belgium in 1922. They have a UK subsidiary

There is definitely no HW storage (checked all rooms, cupboards and even the attic - as it's a bungalow, there is only a finite number of places a tank could be.

Then it must be a combi. Can you post a pic of the boiler?

 

[Djnikon]

Thanks, didn't know about the ACV thing. Could very well be the case as my knowledge of oil boilers is limited to say the least.
I will try get a pic up later today or tonight after work.

It's very odd that I can still get hot water half an hour after the boiler was on.
Even more strange the fact that there is a HW switch if it's directly fed off the boiler.
If the boiler hasn't been on at all and the switch is at OFF then there is no hot water. (I tried this yesterday).

Edit after I clicked your link. My bad, it is ACV in that case as I recognise the Logo from the front of the boiler.
Apologies.