In an earlier contribution to this discussion,
Geronimo W. Christ Esq wrote:


The setting is at about 9 o'clock on the dial which is pretty low.
Even then the boiler cycling is quite bad (off for about 40 seconds,
on for about two minutes continuously). When I set the thermostat
higher than this the cycling is even worse. It is the cycling that
has led me to consider taking action to get the system properly set
up.

Cycling occurs when the rate at which your boiler is producing heat is
greater than the rate at which the radiators and HW cylinder coil can
dissipate it. It should cycle *less* if you turn up the boiler stat because
with the radiators being hotter, they can dissipate more heat. Have you
tried increasing the pump speed?

If the boiler *still* cycles excessively when the house is hot enough in the
coldest weather, it sounds as if it's too big for the job. You can probably
reduce the boiler output a bit by reducing the gas pressure. This will be
explained in the installation manual.

Actually, re-reading what you wrote above - indicating that the boiler is
firing for 120 seconds in every 160 (i.e. 75% of the time) I wouldn't worry
about it if it only does it in steady state conditions. [I would expect the
boiler to run continuously for much longer than that when first starting up
from cold - does it?]
--
Cheers,
Set Square
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