If you increase the boiler stat to max, does the period of short cycling reduce?
Can you prove, via other thermometers that the return pipe and cylinder (at stat location) are reaching the actual temps the system deems them to be reaching?
There is obviously conflict between the boiler overheat stat and the cylinder stat being satisfied, with the ability of the coil to transfer heat to the stored water at the fulcrum!
My physics ain't brilliant but I would expect there is a formula which involves a curve, that describes the diminishing heat transfer rate between the two, over time as the differential reduces!
Defective or worn components, depending on the their age, would also be a factor.
What temperature is your hot water as it comes out of a tap?
Can you prove, via other thermometers that the return pipe and cylinder (at stat location) are reaching the actual temps the system deems them to be reaching?
There is obviously conflict between the boiler overheat stat and the cylinder stat being satisfied, with the ability of the coil to transfer heat to the stored water at the fulcrum!
My physics ain't brilliant but I would expect there is a formula which involves a curve, that describes the diminishing heat transfer rate between the two, over time as the differential reduces!
Defective or worn components, depending on the their age, would also be a factor.
What temperature is your hot water as it comes out of a tap?