"Set Square" wrote in message
...


How does a bypass remove residual heat? For that the pump has to
run so you need pump overrun not bypass. However, you may need a
bypass and pump overrun to cover the situation of all rads with
TRVs (which you shouldn't have) and needing to get rid of some heat
(to the pipe work presumably).

By providing a flow path for the water when the pump is over-running
and all the TRVs and/or zone valves are shut. The residual heat is
actually dissipated by the pipework as the water flows round the
by-pass circuit. If the residual heat can't be carried away from the
boiler, the boiler temperature continues to rise to the point where
its overheat stat trips - which requires manual resetting.

In this scenario the boiler is required by the regs to turn off so the
bypass is only in operation for a very short while

This is true - but the by-pass *must* operate under these conditions,
albeit
for a short period - otherwise the boiler trips. But the by-pass
*shouldn't*
operate at any other time.

I don't have any direct experience of this, but I was speculating that -
with an Alpha pump - it may be difficult (or perhaps even impossible?) to
adjust everything so that the by-pass *only* operates during pump over-run
conditions.

Oh you can adjust an Alpha to do almost anything. You can even make it run
like a normal pump if you want though it gets a lot louder then. But I
found that by setting it a 'bit of a turn' more clockwise than is really
required then I can make the by-pass operate.