In message , Set Square
writes
In an earlier contribution to this discussion,
Rory wrote:

I installed an Alpha during the summer and, now the CH is on, I've
noticed that whenever the Suprima re-fires after the boiler stat has
shut it down, then the Alpha speeds up before gradually settling down
again. This means that, contrary to the way it's supposed to work,
the noise through our TRV's is quite loud, and all the more noticeable
because it comes & goes each time the boiler cycles. The Alpha is set
at the lowest point on its variable scale.
I *think* that what's happening is that the Suprima is momentarily
disconnecting the pump as the boiler fires? If this is true, then the
pump is acting correctly.
Is this (disconnection of the pump) a known *bug* with the Suprima?
Thanks
Rory

I would hazard a guess that the boiler is controlling the pump, and that it
has a pump over-run stat to stop the boiler from overheating.

Well not a stat, it's software controlled and pump overrun in a Suprima
is 20 minutes

As I explained when he posted this question the first time, the pump is
pulsed at the beginning of a heating cycle

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--
geoff