Oil fired boilers in general do not need ABVs as the Hx holds 20/25 litres of water which acts as a buffer so when the boiler+ pump cuts out, the water temperature (from a target temp of say 70C) will not rise > 90C/95C, a long way from the hi limit lockout of 113C. Gas boilers have a Hx content of only a few litres and this is why they have a timed pump overrun after all zone valves shut, the water then has no where to go so need a ABV.