"Andy Hall" wrote in message
...

BTW, how does the Alpha know when to restart? Does it "poll" at a certain
frequency to check the resistance?

The Alpha doesn't stop and start of
its own accord, it simply winds
down to a lower power with increasing resistance.

I was informed by a Grundfos rep when they first came out that is stopped.
Maybe he didn't know too much as it was a brand new product.

The purpose of the flow switch would
have to be to detect when TRVs
had closed to a sufficient point that an
automatic valve on a bypass
opens - i.e. flow starts through the bypass
and the switch operates.

An auto by-pass would not be opened by an Alpha. The valve requires pump
pressure to open it. When the Alpha detects pressure it reduced the speed
thinking TRVs are cloosed down. A permanent by-pass is the best option.
The flow switch detecting if the TRVs are closed should not be in the
circuit of the by-pass.

This would need a relay, since the logic is wrong, and also I wonder
how the bypass needed for the boiler would work. That would need an
extra time switch or relays to work properly I think since it needs to
run uncondtionally vis-a-vis what the CH is doing.

A flow switch would switch off the boiler/burner, maybe via thermostat
terminals. The Alpha can be left to run as



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