Is my Navien boiler behaving as expected?

[ShaunCorbs]

Any other potential issues that could be responsible?

Could be supply pipes from the boiler not fully clear / restriction as I would say that coil would easy heat the cylinder up within the hour

 

[Oilyjoe]

Could be supply pipes from the boiler not fully clear / restriction as I would say that coil would easy heat the cylinder up within the hour

You might be right. The last boiler used 28mm pipe and this uses 22mm supply/return but connecting to the existing 28mm pipe into the house

 

[RoryD]

Wondering if the Pump is up to scratch?... 10m?