"John" wrote in message
...

As the season warms up the duty
cycle of the boiler will become more off than on and the true efficiency
will be much lower, eventually in summer the only load will be hot water.
Under these circumstances switching on from cold will show a steady demand
to heat the cylinder but once it is heated only small burst of
replenishment
heat (subject to the cylinder thermostat) will be required. Under these
conditions you will obviously not get the same efficiency as during winter
with full load demand.

Using a quick recovery coil cylinder that take all the boilers output and
two cyclidner stats, boiler cycling is eliminated, and efficiency is "very"
high heating DHW.