DHW for extension

[Silage]

@Nickfromwales, just thinking about ordering (cylinders2go?). Presume that the buffer doesn't need a separate expansion tank or prv as it uses the one on the system boiler? Still wondering if a TS would be a simpler and cheaper install?

[Nickfromwales]

4 minutes ago, Silage said:

@Nickfromwales, just thinking about ordering (cylinders2go?). Presume that the buffer doesn't need a separate expansion tank or prv as it uses the one on the system boiler? Still wondering if a TS would be a simpler and cheaper install?

Expansion volume is relative to the volume of water it services. A typical system boiler will have an expansion vessel ( EV ) capable of servicing circa 10 average radiators plus the connective pipework. The boiler manufacturer will be able to tell you the size of the EV and the volume of primary water it's suited to, with higher volumes / temperatures requiring additional expansion accordingly. 

[Silage]

Thanks @Nickfromwales I'll ask them. I'm struggling a bit to physically incorporate separate zone valves for new and old rads due to existing pipe runs  Do you think they are necessary? Would rad TMV's be ok instead? If you have time a schematic would help me confirm what I need. Thanks.