Michael Chare wrote:

On 22/11/2017 20:55, Cynic wrote:
I've got a friend who has a Firebird oil fired combi about 15 years old.
It's been a reliable unit with the exception of suffering a few failures
of the 1/2" flow switch that detects when a hot tap is opened and starts
the pump feeding primary hot water to the plate heat exchanger. There
was a component change of type of switch from a microswitch to a reed
type a few years ago accompanied by a slight circuit change so the reed
switched the coil of an octal plug in relay. The paddle operated reed
switches in a plastic body are prone to failure in the nc (on) state
which results in the central heating pump being inhibited. I replaced
one for her a few days ago and it's failed again already. It shows
continuity in the on position but has a resistive path in the off
position. I'm guessing it's got water in the internal (sealed)
connections. Whatever the reason it's holding the relay energised. I'd
like to find a robust suitable 1/2" flow switch capable of switching a
grundfos 15-60 and rated for mains cold water pressure, say 6 bar or
more.. Anyone able to suggest a suitable make and model, economically
priced and available in the UK?


I use one of these:

http://uk.farnell.com/gentech-intern...h-brass-ac-10b
ar/dp/1006768?CMP=i-bf9f-00001000

but it might well be difficult to mount inside a boiler. I like it ecause
bthere is nothing to leek, unlike the previous device I had.

There is a wide choice of flow switches on ebay.

Worcester Bosch use a flow switch in their Heatslave oil boilers. The
switch is not very big. You might find one to look at an appropriate
supplier.
As long as you run another cold feed to the filling loop the supply to
the hot water heat exchanger can come from outside the boiler via the
flow switch and a flying lead from the external flow switch can be
connected into the control box (which is the existing arrangement, but a
shorter lead).

--

Roger Hayter