On Fri, 15 Feb 2013 17:26:43 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Bob Minchin wrote:
Dave Plowman (News) wrote:
Seems it's a manometer. Presumably to work the gauge which shows the
water pressure?

Possibly but as it goes to the PCB, it will measure the system pressure
and shut down the boiler if it falls below a prescribed limit.

If the pressure gauge is electronic, the same sensor might be used for
the display but otherwise a simple selef contained mechanical pressure
gauge is probably used for the display.

The term manometer is more associated with measuring gas pressures which
is not likely to be monitored by your boiler but also could be measuring
fan air pressure which will be monitored by the control system.

A manometer is simply a device for measuring gas or liquid pressure.

Fluid pressure then.

In this case it pokes into the water return to the boiler, so I'd guess it
simply measures the water pressure - being a pressurized system. Won't
know if it cuts off the boiler if the pressure is too low until I change
it when the new one arrives on Monday. It's then I'll find all it needed
was a new O ring. ;-)